Air Conditioning and Pressurization

Pressurized air from the pneumatic system is used for air conditioning and pressurization.
On the ground, air for the air conditioning system can be obtained from an external ground
source connected to the aircraft, from the APU or from the engines. In flight only the
engines supply air for pressurization and air conditioning.

Air Conditioning Systems

The aircraft has two identical air conditioning systems, designed to

operate independently or in parallel. Normally the right system operates
with bleed air from the right engine and controls the temperature of the
passenger cabin. The left system operates with air bleed from the left
engine and controls the cockpit temperature. Any system is capable of
supplying the requirements of both cabins.

Air systems are protected from overtemperature conditions by sensors

that shut down the system. The flow and pressure regulating valve will
close, preventing air from passing to the respective system when the
discharge temperatures of the compressor or turbine inlet or in the
supply duct are excessive.

Air Distribution

The cold air is directed to the individual exits of each passenger and
each pilot. Each outlet can be adjusted in its direction and flow. The
conditioned air from the system passes through the mixing chamber to
distribute it to the passenger and pilot cabins. Air for the passenger
compartment is continuously discharged through the outlets under the
luggage racks. A recirculating fan located forward of the rear
pressurization bulkhead returns cabin air to the overhead ducts for
recirculation. The recirculating fan has no control or indication in the
cockpit and only works in flight.
Temperature Control
Temperatur
The temperature is controlled from the pilot compartment. Movement of the CKPIT
TEMP and CABIN TEMP selector in AUTO mode selects and automatically regulates
the temperature.

When operating in MANUAL mode, the CKPIT TEMP and CABIN TEMP selectors are
spring-loaded to the STOP position and must be momentarily held in HOT or COLD
until the desired temperature is obtained.

A CABIN TEMP indicator shows the temperature in the passenger compartment or the
air supply duct.

Radio Rack Cooling

Cooling of the radio rack is provided by air conditioning from the pilot compartment.
When the RADIO RACK switch is in FAN, the conditioned air that passes through
the radio rack is expelled under the floor of the front warehouse for heating. When
the RADIO RACK switch is in VENTURI, no heating is provided to the front hold
and air is expelled out through the venturi.

A secondary fan in the radio rack, located in the racks' cooling ducts, will
automatically turn on if the primary fan fails in flight. In ground mode, the primary
and secondary fans will operate when the RADIO RACK switch is in either the FAN
or VENTURI position. A RADIO FAN OFF annunciation will light only when both
fans fail in flight or when the primary fan has failed on the ground.

APU on the ground

The APU can be used to supply air conditioning to the pilot and passenger
compartments while the aircraft is on the ground. The APU AIR switch, in the ON
position, powers the bleed air control valve by opening it, delivering air to the
pneumatic system. The AIR COND COLDER position provides an increase in
differential pressure for additional cooling. The OFF position discontinues power to
the air control valve, closing it.

When the aircraft is on the ground and the throttles reduced, placing the switch in ON or
AIR COND COLDER also activates a solenoid that causes the air conditioning pressure
regulator to move to the fully open position. In this mode, all of the APU's air pressure is
delivered to increase cooling capacity. When advancing the throttles or in flight, it will
revert the system to normal regulation mode by deactivating the solenoid.

Pressurization Outflow Va

Pressurization is provided by a controlled flow of air bleed from the engines, which
passes through the air conditioning system and is then conducted to the pressurized
areas. Desired pressurization levels are maintained by regulating the release of
compressed air through the outflow valve. Normally, the outflow valve is automatically
regulated by a dual automatic pressurization system to control cabin pressure from
takeoff to landing.

For automatic operation of the outflow valve the CABIN ALT control lever must be up.
The control wheel will rotate as it automatically adjusts pressurization. A position
indicator, next to the wheel, will move to indicate the position of the valve.

For manual operation of the outflow valve the CABIN ALT control lever must be down.
To manually maintain pressurization, press the wheel and rotate it in the desired
direction. The indicator will move in the same direction to indicate the valve position.
Pressuriza
Relief valves are installed to protect the airframe from maximum pressure or pressure
from a possible rupture of a wing anti-icing system duct. The relief valves will limit the
cabin differential to between 7.95 and 8.27 psi. The maximum differential limit is 8.32
psi. A negative differential is relieved by the inward movement of the galley and access
door seals, and a relief valve in the rear pressurization bulkhead.

Outflow valve externa

With the aircraft on the ground, the dual pressurization system will begin to
pressurize the cabin when the throttles are positioned for takeoff, a 60 second
timer is activated. In the case of aborting the takeoff, the cabin will
automatically begin to depressurize when the throttles are delayed. If the
airplane does not go into flight mode within 60 seconds after the throttles
have been advanced, the cabin will depressurize. With the aircraft in flight,
cabin pressure is automatically controlled. During climb, cruise and descent
the cabin will maintain the programmed profile using the programmed
altitude, which is a function of the altitude of the aircraft.

The dual automatic pressurization system consists of two identical but

independent systems, powered by different electrical sources that are
controlled by the cabin pressure selector panel. One system has primary
control while the other serves as backup.

If a manual or automatic transfer occurs before landing, it will result in a

blocking of subsequent automatic transfers or system exchange after landing.
The TRANSFR LOCKOUT and STDBY ON lights will come on and do not
need to be reset. This will help maintenance identify which system failed.

If the performance of the backup system (STDBY) is not satisfactory, the primary
system can be reselected by turning the selector switch to STDBY and then back
to PRIMARY. Manual selection allows you to select the system that has the best
performance. Do not reset the TRANSFR LOCKOUT light. This inhibits any
automatic transfer of the system that works best.

Limitations

Maximum normal differential pressure...................................7.77 psi

Maximum relief valve differential pressure...................8.32 psi
Maximum air supply pressure................................27 psi (engines), 31-40 psi (APU
air In use)
Augmentation valve regulating (air conditioning)...21 psi
Pneumatic pressure (yellow arc)....................................20 psi
Minimum pneumatic pressure for anti-icing................................20 psi
 Air conditioners are primarily cooling installations that, so to speak, complement the
heating of standard equipment and, together with it, completely air-condition the vehicle.
The air conditioner installed in the vehicle is integrated into the ventilation and heating
system. Climatizing or conditioning the air means regulating the temperature, humidity,
purity and circulation of the air. An air conditioner in the vehicle cools the air and removes
moisture and dust from it. By means of the manual or automatically combined cooling and
heating units, the driver can regulate the temperature inside the vehicle as he chooses.

{mosgoogle3 right}The air conditioner works on the principle of the compressor

refrigeration system (refrigerator) and consists of the following main elements:

1. Compressor —-------------- built into the engine

2. Condenser —----------- installed in front of the radiator

3. Evaporator —------------- placed in front of the heating body

4. Accumulator —------------- installed in the suction pipe

5. Orifice valve —------ installed in the liquid, in front of the evaporator

6. Various regulating bodies, flexible pipes, refrigerant.

Principles of operation of air conditioning

The operation of the air conditioner is subject to three natural laws:

1st law — Heat always moves from the hotter object to the colder object. Heat
is a form of energy; Temperature is a measure for its intensity.

2nd law — To convert a liquid into vapor, heat is necessary.

If, for example, water boils on a burner, it absorbs a large amount of heat
without changing its temperature as it evaporates.

If, on the other hand, heat is extracted from the steam, then the steam
condenses and becomes a liquid.
The temperature at which water boils, or water vapor condenses, depends on
pressure. As the pressure increases, the boiling temperature increases.
3rd law — When you compress a gas, its temperature and pressure increase.

Example: When the piston of a Diesel engine moves upward, it compresses the
air. When compressed, a high temperature is generated which, if fuel is injected
into the cylinder, ignites it immediately.

The fundamental refrigeration cycle in which the aforementioned laws are

applied is carried out in the following way:

1. The liquid refrigerant absorbs heat from the environment when it evaporates
(1st and 2nd laws).

2. The hot vapor is compressed and reaches a temperature higher than that of
the ambient air (3rd law).

3. The ambient air (which is colder) absorbs heat and condenses the vapor,
turning it into liquid (1st and 3rd laws).
4. The liquid flows to the starting point of the cycle and is used again.

The compressor, by means of its pumping effect through the accumulator

(which in turn acts as a liquid separator), draws refrigerant vapor at low
pressure and low temperature from the evaporator and compresses this vapor
at a higher pressure. and at a higher temperature.

The liquid separator is necessary because with the vapor of the refrigerant
agent, traces of unevaporated liquid can also be carried along, which, if they
reached the compressor, would destroy it. The remaining liquid can completely
evaporate in the accumulator. This is then sucked in by the compressor
together with the normal refrigerant vapor. Any oil from the circulation that may
be in the accumulator is led back to the system through an oil hole located at
the bottom of the accumulator.
From the compressor, the "hot" refrigerant vapor is compressed to the condenser (heat
exchanger) through the hot gas pipe. The colder outside air passes through the condenser
and extracts heat from the refrigerant vapor.

In the condenser, the refrigerant vapor is cooled to below the boiling point of
the refrigerant due to the heat extracted from it and condenses to form a liquid.
The liquid agent passes from the condenser, through the liquid pipe, to the
orifice valve, which, due to its calibrated passage (separation point between
high and low pressure), takes care of the following three functions.

1.- The orifice valve regulates the flow of the refrigerant (amount of refrigerant)
through the evaporator.

2.- Due to its section for the passage of the refrigerant, which is constructively
fixed and not variable, the orifice valve generates a low pressure in the
evaporator. As a result of the pressure drop in the evaporator, the liquid
refrigerant can evaporate more easily. As a consequence of the evaporation of
the refrigerant agent and the absorption of heat associated with evaporation,
the temperature on the exterior evaporation surfaces necessarily drops, so that
the air passing through them is cooled.

3.- The orifice valve maintains a pressure in the liquid condensed refrigerant, so
that it remains liquid.

Due to the invariable cross-section of the orifice valve, with the compressor
running the same amount of refrigerant always reaches the evaporator, i.e. the
cooling performance cannot be regulated through the orifice valve. In this air
conditioner, the cooling performance can only be regulated by means of a
thermostat, which, through an electromagnetic coupling, disconnects or
activates the compressor.

The thermostat probe (sensitive element) is firmly connected by means of a

capillary tube, behind the orifice valve, to the evaporator connection tube and
receives any temperature variation on the low pressure side, that is, in the
evaporator . So that the connection point cannot be affected by the heat of the
motor, it is well shielded by means of closed insulation.

As a result of the vaporization of the refrigerant, the evaporator cools, and

simultaneously also the connection pipe behind the orifice valve.

The gas in the probe and capillary tube also cools, compressing it, and
consequently reducing the pressure in the thermostat membrane chamber. At a
certain pressure – which corresponds to a certain temperature – the connection
contacts open. The compressor is disconnected through the electromagnetic
coupling sandwiched between the drive pulley and the compressor. In cold
weather, the air conditioner is switched off via the magnetic coupling. It would
not be profitable to keep the system constantly running. With the magnetic
coupling disconnected, the power transmission is separated from the motor and
the V-belt pulley rotates freely, so the motor is not subjected to the load of the
operating compressor.

As soon as the temperature in the evaporator rises to a certain value, the

contacts in the thermostat close again due to the rise in pressure in the
capillary tube. Between these two fixed points, the thermostat and
consequently the air conditioner work continuously and automatically. In order
for the refrigerant in circulation not to be altered by moisture particles - water -
all traces of humidity must be extracted from it. In the accumulator,
sandwiched between the evaporator and the compressor, there is a chemical
product in the suction pipe which, thanks to its specific qualities, binds the
humidity in the refrigerant circuit.

To protect the air conditioner against overpressure or shortage of refrigerant

A high pressure safety switch and a low pressure safety switch have been
connected to the refrigerant pipe. The connection of the high-pressure safety
switch is also used to connect the high-pressure measuring line when carrying
out maintenance or control work. The high pressure safety switch shuts off the
compressor if the pressure in the air conditioner reaches an excessively high
value that could endanger the system.

An impermissible increase in pressure may be a consequence of the additional

blower upstream of the condenser having stopped working, or a dirty condenser,
or extraordinarily high outside temperatures, or extreme engine overload. As
soon as the pressure in the air conditioner drops to normal values, the high
pressure safety switch automatically switches the compressor back on.

The low pressure safety switch switches off the compressor as soon as the
pressure in the air conditioner drops below a certain value. In contrast to the
high pressure safety switch, the low pressure safety switch does not
automatically reconnect the compressor, as the cause of a pressure drop is
usually a shortage of agent. Fridge.

In such a case, the leak or leaks must be found in the entire air conditioner,
repaired, and refrigerant refilled. Since there are leaks, in addition to the
refrigerant leaking out, the oil can also leak out, disconnecting the compressor
is a safety measure to avoid damage to it as a result of a lack of oil.

Humidity in an air conditioner Important!

Moisture in air conditioners altogether causes more problems and breakdowns
than all other causes combined.

It must be fundamentally differentiated between invisible humidity and visible

humidity.

Visible humidity refers to moisture that can be seen with the naked eye, such as
tiny droplets, fogging, evaporation, etc.

Water vapor that cannot be seen is called invisible humidity. Its proportion in
the air is designated "relative air humidity." This invisible humidity is what
causes most complaints about air conditioners.

The consequences of humidity are described in detail below.

* As the first phenomenon, we can mention the "freezing" of tiny water

particles.

Moisture enters the refrigerant, is carried with it in the form of a light mist and
forms small ice crystals on the orifice valve (expansion valve).

These crystals can hinder or even prevent the flow of the refrigerant, so that the
refrigeration stops working completely or partially. Since, on the other hand, the
orifice valve heats up when the refrigerant flow is low, the ice crystals melt and
can pass through the valve. In this way, the refrigerant circulates again until
this moisture returns to the valve and forms ice crystals again. The
consequence is that the cooling is irregular.

Whether this system blocking effect occurs or not depends on the amount of
humidity and ice crystals that have formed.

* Moisture can also cause metal parts to rust, which is all the more unpleasant
since the damage can only be noticed when the oxidation process is already
very advanced.

A high vacuum pump is the most effective element that can remove all moisture
from the hermetically closed installation, because it forms a vacuum such that
the water reaches the boiling point. Water that becomes a gaseous medium
(water vapor) is removed from the installation by the vacuum pump as if it were
ordinary air.

refrigerant agent

Description
The refrigerant agent used has the chemical name "Dichlorodifluoromethane"
(CC12 F2). It is known under the name "Frigen 12" (R-12); As has already been
indicated repeatedly, in some countries it is also called "Freon 12" .

The refrigerant agent is highly refined so that it is free of all types of impurities.

Any type of refrigerant agent requires careful handling. When working with
refrigerant, certain rules must be taken into account and followed to avoid
serious personal injury.

All safety refrigeration agents with the name Frigen are non-flammable and do
not form any explosive mixture in conjunction with air in any proportion.

Frigen is not poisonous , does not irritate the mucous membranes and is
odorless in concentrations of up to approx. 20 Vol. % in the air.

Since one of the essential premises for perfect and fault-free operation of an air
conditioner is a sufficiently low humidity content in the refrigerant circuit, the
humidity content of the Frigen (Freon) is permanently monitored and controlled
during the process. manufacturing and packaging for shipment. All containers
for shipment are regularly inspected, carefully cleaned, dried and evacuated, in
order to guarantee their high degree of purity.

The moisture content of Frigen (Freon) is not more than 10 mg/kg (= 0.001%). It
is therefore well below the limit at which it could cause freezing or corrosion;
That is to say, this humidity cannot cause any damage if, on the other hand, by
drying the installation perfectly and using dry oils for the refrigerant, excessive
additional amounts of humidity are not incorporated.

Under the normal working conditions of air conditioners, the metals and alloys
that are normally used are not attacked by Frigen (Freon) in either the liquid or
gaseous state.

Note: today this refrigerant agent is not used due to its negative effect (it
causes what is called the "greenhouse effect" in the atmosphere). It has been
replaced by R-134a .

Under no circumstances will R-12 and R-134a refrigerant agents be exchanged

or mixed with each other.!!!

Oil for refrigerant

Function

Lubrication of the seals, the intermediate parts of the seals and the moving
parts of the compressor.

Description

The refrigerant oil used in air conditioners is highly refined and dehydrated, so
that it is perfectly compatible with the refrigerant Frigen (Freon) R 12. The oil
for the refrigerant is supplied by the Spare Parts and Accessories Department.
The oil for the refrigerant must be poured directly into the refrigerant on the
suction side of the compressor. The refrigerant agent carries it with it
throughout the entire system. The procedures for checking and topping up the
oil for the refrigerant are detailed below. It is very important that the system is
always supplied with the prescribed amount of oil for the refrigerant.

Air conditioner control in accident vehicles

In vehicles with an air conditioner, in the event of an accident, a visual

inspection of the various component parts of the conditioner must be carried
out as soon as possible. This is especially important since parts or elements of
the system that are under pressure may have been damaged, which under
certain circumstances may pose an additional danger.

Determining which parts of the air conditioner need to be replaced or repaired

depends on the extent of the damage and the length of time the installation has
been exposed to outside air. The longer the open installation has been exposed
to outside air, the greater the danger of air, moisture or dirt entering it. As every
accident is totally different, no specific rules can be cited regarding the
controls, verifications and repairs that must be carried out after an accident.
The various stages of work to be carried out must be determined in their
entirety by the refrigeration technique expert in each of the cases that arise.

The following indications can serve as a guideline for the examination or control
of accident vehicles equipped with air conditioning:

1. Remove, or possibly cut, the V-belt so that, with the engine running, the air
conditioner does not operate.
2. Carry out a visual inspection in order to verify the extent and type of damage,
in the following

items:

Condenser. Due to its type of construction, no repair work can be carried out on
the refrigerant-conducting parts of the condenser; If any of these are damaged,
the capacitor must be replaced.

Compressor. Inspect the compressor for visible damage. If you have them,
dismantle it and repair it.

Accumulator. If there is any sign that the accumulator has internal damage, or
that welded pipes or joints have been broken or torn, the accumulator must be
replaced. The same applies if the installation has been open for a long time.

Evaporator. Check the evaporator and its box for damage. Replace damaged
parts.

Union pipes. Check the connecting pipes for damage. Replace damaged parts.

Command elements. Check the control elements and electrical conduits for
damage. Repair damaged parts or replace them completely.

Air conditioner control

1 . Leak control. Check all pipes, joints, connections and elements with a leak
detector to check for possible refrigerant leaks.

2 . Performance control. Check air temperatures and refrigerant pressures to

verify if the system is working satisfactorily.

3 . Engine - idle. The number of engine revolutions must be within the specified
limits.

4 . Heating. If the heating is switched off, there should be no air passage

through the heater core.

5 . Bodywork. Examine the doors, windows and dashboard wall for points or
areas that do not seal tightly, and, if necessary, eliminate these airtight defects.
6 . Air ducts. All flexible air distribution tubes, as well as the channels, must be
perfectly joined and without leaks or narrowing. The blower must work perfectly
at all its connection levels.

7 . Electrical installations. The compressor coupling has to start the compressor

when necessary. The electrical cables must be perfectly routed.

8 . Drive belt. The drive belt must have the correct tension and be in good
condition.

9 . Flexible refrigerant tubes. Flexible hoses and pipes must not have any
constrictions or constrictions; They must also be protected so that they cannot
rub against sharp metal surfaces, moving parts, or very hot engine parts.

10 . Evaporator. The condensation outlet must not have any impediment.

eleven . Condenser. The front face of the condenser must be free of all
obstructions, such as leaves, insects and dirt. Also the space between the
condenser and the radiator must be free and clean.

12 . Regulation facilities. Bowden cables must be adjusted firmly and correctly.

The control levers must be able to be moved easily.

Tools and equipment

To repair and control an air conditioner, special control instruments and tools
are required. Without these tools it is not possible to carry out repair or
diagnosis work.

A Service Station is essential for maintenance work on air conditioners, as well

as a leak detector to verify the existence of any leaks.

The Service Station must be equipped with a vacuum pump, a set of measuring
instruments for suction pressure and high pressure, various valves and a
calibrated filling cylinder (test tube) for the refrigerant.

Every Service Station is provided with a detailed Instruction Manual and a work
diagram, based on which the Station can be used to repair an air conditioner.

Every leak detector is provided with an Instruction Manual based on which the
device must be used.
detector.

With this mobile service station the following jobs can be carried out:

* Empty air conditioner

* Prepare cooling agent

* Evacuate air conditioner

* Fill air conditioner

* Measure pressures in the refrigerant circuit

Precautions for storing and installing air conditioner parts

To ensure a high degree of cleanliness and reliability of the air conditioner

parts, the following measures must be observed when handling these parts.

1. All sets are cleaned before shipping and packed tightly. Shipping caps or
covers should only be removed when installing parts, immediately prior to
connection.
2. To avoid moisture condensation in the refrigerant pipes, they must be at the
same temperature as the environment where they are working before removing
the pipes.

shipping caps or covers.

3. A fully or partially assembled system should not remain unclosed for longer
than necessary.

4. Precautionary measures must be taken to avoid damaging the connections

and joining parts.

5. To remove grease or dirt, only a cloth soaked in alcohol should be used.

6. Parts whose condition raises doubts should not be used.

7. If there is dirt, grease or moisture in the pipes, they must be replaced or

cleaned and then rinsed with refrigerant. The same applies to pipes in which
protective caps or covers are missing.
8. If you have to clean the inside of any part, only Frigen R 12 refrigerant agent
should be used (which, as has already been indicated repeatedly, is also called
Freon in some countries).

9. Before assembly, a small amount of refrigerant must be applied to all

connection points of pipes or hoses and to the O-rings (seal rings).

10. To prevent the pieces that are joined from being twisted or bent, when
tightening, the piece that does not rotate must be held with a wrench.

11. To avoid deformation of the pipes or flange seats as a result of too high a
torque, the joints should only be tightened up to the specified torque.

Checking the tightness of the refrigerant circuit

Checking the tightness of the refrigerant circuit using a leak detector is one of
the most important procedures and must be carried out conscientiously.

Leaks can form at any point in the system, such as at joints, threads, in the
compressor, in the measuring instrument, in the filling valves, in the evaporator,
in the condenser and in the accumulator.

Since the refrigerant is heavier than air, the lowest point of the area where
leaks could possibly occur must be monitored. The leak detector probe must
always be close to the underside of the joint areas.
If a leak is detected at a joint, it must be eliminated by tightening the joint in
question, or, if necessary, by replacing the O-ring sealing ring. The control must
then be repeated.

When checking for possible leaks, the joints and threads must be free of
unnecessary oil, in order to eliminate the possibility of false results as a result
of the absorption of refrigerant in the oil.

If the joints have been retightened and it is foreseeable that traces of

refrigerant remain in the engine compartment or on the bodywork, these must
be removed by blowing with compressed air. Cigarette smoke can also lead to
false results, e| refrigerant or other vapors in the

proximities.

The accuracy of the leak monitoring results depends on the sensitivity of the
leak detector, whether the monitoring is carried out at the lowest points of
possible leaks, and whether the external surfaces are well cleaned. In addition,
the control must be carried out in a place where there is sufficient ventilation to
the

to ensure that the air in the environment is clean. The vehicle engine must not
be running.

Control of oil content

Pay attention to the accident prevention regulations!

At first, the entire oil charge is in the compressor, or, respectively, in the
refrigerant pipe.

After the air conditioner has been put into operation, the oil circulates together
with the refrigerant throughout the entire system.

If, for example, the compressor is dismantled, the entire oil content is never
found in it, but only the partial amount corresponding to the compressor.

If a large amount of oil has been lost, the corresponding amount of new oil must
be replaced in the system.

Normally it is not necessary to control the oil charge in the air conditioner.
Generally, an oil quantity check should only be carried out if there are
indications that there has been a large loss.
Oil loss can be caused by:

* breakage of a flexible refrigerant tube

* major leak in a connecting piece

* compressor gasket with a big leak

* damage to component parts of the system as a result of an accident

If oil has leaked from the system, proceed as follows:

1. Run the air conditioner for about 10 minutes.

2. Disassemble the compressor.

3. Completely drain the oil from the compressor. To do this, turn the compressor
over and rotate the compressor shaft.

4. Pour a load of oil directly into the compressor again with the help of a small
funnel.

Pay attention so that the compressor inlet is not completely blocked so that air
can escape.

Fill oil with the installation closed

If it is necessary to add oil to the installed compressor, the system must not be
full of refrigerant. If necessary, the refrigerant charge must be emptied.

Connect the service instrument (Service Station) to the respective connections

based on its manufacturer's instructions.

Pour clean oil for the refrigerant into the oil tank.

When the vacuum pump is connected, atmospheric pressure draws the oil into
the system. When the corresponding amount of oil has been sucked in, close the
valve on the oil tank, but keeping the vacuum pump running.

It must be taken into account that when adding oil, a certain amount of it
remains attached to the oil tank and the pipe from the instrument to the
compressor; This amount - which is different depending on the brand of the
Service Station - must be added to the load of oil to be added.

When replacing parts such as the evaporator, condenser or accumulator, the

corresponding amount of oil can be poured directly into the part.

When replacing the condenser it is not necessary to add new oil, since the new
compressor is supplied with the prescribed amount of oil.

Draining the air conditioner

Before emptying the air conditioner, for safety reasons, the possible existence
of leaks must be checked at all joint or connection points using the
recommended electronic leak detector.

If any leaks are not located and sealed before emptying, air and moisture may
be sucked into the system when it is subsequently evacuated.

With the vacuum pump running, close the shut-off valves and then disconnect
the pump.

Next, carefully observe the vacuum gauge to check if the vacuum remains
constant with the pump disconnected.

If the vacuum remains constant for approx. 2 minutes, the system can be filled
with the prescribed amount of refrigerant.

{mosgoogle right}Filling the air conditioner

The air conditioner can only be filled if it has been previously evacuated.

Check the level of the refrigerant in the glass of the filling cylinder depending on
the pressure in the cylinder. If necessary, correct the amount of refrigerant.

Opening the valves provided for this purpose, allow the refrigerant to flow into
the evacuated air conditioner.

Observation:

If the full load of refrigerant from the filling cylinder does not enter the air
conditioner, close the high pressure valve at the Filling Station.
Start the engine and connect the air conditioner.

Due to the pressure drop generated by the operating compressor on the suction
side, the remaining amount of refrigerant is sucked out of the filling cylinder and
fed into the refrigerant circuit.

Air conditioner control in operation

Let the air conditioner operate for a few minutes in the maximum cooling
position, maximum blower revolutions and engine revolutions of 1500 min^1
(rpm).

After the system has stabilized, the high pressure gauge and the low pressure
gauge must indicate the specified values. Place your hand in the exit area of the
nozzles through which the refrigerated air comes out to notice that, in fact, it
comes out cold.

Next, unscrew the flexible measurement tubes from their connections.

The first part of the course ends

Comment that we have reviewed the principle of operation, characteristics and

maintenance work on air conditioning systems. The topics discussed
correspond to the first first generation air conditioning systems, so to speak,
the change of refrigerant agent (R-134a for R-12) was not the only important
change, other changes were also made that we will see in the next chapter of
the course, as well as the operation of the different elements that make up the
air conditioning system.

The second part of the car air conditioning course begins

Description of the different components of the air conditioning system

Compressor
The compressor is attached to the engine by means of a support and is driven
by a V-belt.

The kinematic connection of force with the motor takes place through a
magnetic coupling that separates said connection of force when the current is
disconnected. The electromagnetic coupling is activated when the air
conditioning installation is connected; That is, the compressor works as long as
the air conditioning installation is connected, thus avoiding alterations due to
load changes.

The compressor has a variable displacement through which it is possible to

regulate the cooling power. The displacement regulation is obtained through a
Wobble plate with a variable adjustment angle and the five pistons arranged
axially and driven by the Wobble plate.

The adjustment angle is modified depending on the power needed from the air
conditioner; That is, depending on the amount of refrigerant to be supplied to
the evaporator, taking advantage of the difference between the internal
pressure of the compressor casing and the pressure on the high-pressure side of
the refrigerant circuit. This takes place with the help of pressure forces acting
on the front and bottom of the pistons.

The pressure existing on the high pressure side in the refrigerant circuit presses
the front of piston A and the pressure of the compressor casing presses the
bottom of piston B.
As the ratio of these two forces varies, the pistons can move in the direction
where the pressure exerted is lower. Since the plungers are attached to the
Wobble plates, they press them in the direction of the lowest pressure. As soon
as the forces exerted have been balanced, the Wobble plate is held in position.

The Wobble plate is housed on one side in a sliding bearing that allows it to
oscillate, and on the other side it can move along a guide bar. When the
compressor is running, the oscillating part of the plate does not rotate. Only the
center of the Wobble plate is rotated by the drive shaft.

Since the Wobble plate is at almost a right angle to its bearings, it oscillates
only slightly, the stroke of the piston is the minimum, with almost no passage of
agent taking place.

refrigerant.

If, due to higher pressure, the Wobble plate at the front of the piston is
displaced to the maximum, the plate oscillates more intensely, the piston stroke
increases and the power supply of the compressor reaches its maximum
degree.

Since the pressure on the high pressure side of the cooling agent circuit is
almost constant, the force exerted by the front of the piston is also almost
constant. Only by varying the counterforce exerted by the bottom of the plunger;
That is, by increasing or reducing the pressure inside the casing, the adjustment
angle is modified.

The pressure inside the casing (compressor) is regulated with the control valve
mounted on the rear side of the compressor.
A metallic membrane body 5 is arranged in the valve, with depression, on which
the pressure existing on the low pressure side of the cooling agent circuit acts.

Higher pressure on the low pressure side compresses the membrane body,
expanding as the pressure is reduced. The compression and expansion of the
membrane body acts on the valve ball 2 and the step reducer 4, both connected
through the valve stem 3, opening or closing by the pressure of the spring 1 or
the back pressure of the membrane body.

The valve ball regulates the increase and decrease of step to decrease the
internal pressure of the compressor casing.

The operation of the regulating valve when more or less power flow is needed is
as follows:

* When a lot of power is needed : the high pressure on the low pressure side
acts on the membrane body and compresses it. With this, the valve ball closes
the high pressure passage and opens at the same time the reduction of the
passage. The cooling agent found in the compressor casing can exit through the
suction side, thus reducing the pressure inside the casing.

The adjustment angle of the Wobble plate is widened, thus increasing the stroke
of the plunger.

The compressor displacement is thus regulated to maximum power.

* When little power is needed : the low pressure on the low pressure side acts
on the membrane body, allowing it to expand, thereby closing the reduction of
the passage. The refrigerant vapor present in the compressor housing cannot
escape from the suction side. The valve ball opens the inlet for the high-
pressure cooling agent, thereby increasing the pressure inside the housing. The
adjustment angle of the Wobbler plate is flattened and the plunger stroke is
reduced.

The compressor operates at minimum displacement at minimum power.

The use of this type of V 5 compressor, which has a variable displacement,

avoids having to connect and disconnect the compressor according to the
power needs of the refrigeration circuit using a thermostat (as explained in the
principle of operation of the air conditioning in the first part of the course).

The cooling power of the air conditioning installation is regulated by modifying

the variable displacement of the V 5 compressor. In this way, connection
shocks are avoided when connecting and disconnecting the compressor as was
done in older air conditioning installations, which controlled the refrigerant
power through a thermostat, connecting and disconnecting the compressor
through its magnetic coupling.

Through this type of regulation, the air conditioning installation works more
uniformly, calmer and more economically and its cooling power is permanently
adjusted to the cooling needs.

On the rear side of the compressor are the high-pressure safety switch, the
additional turbine switch and the high-pressure safety valve.
Condenser

The air conditioning system condenser is located in front of the engine cooling
radiator.

As a general rule, condenser temperatures range between 50°C and 93°C.

Consequently, the overpressures range between 1050 kPa and 2100 kPa.
Abnormally excessive pressures may occur if the air flow is not sufficient (for
example, due to dirt in the condenser or crushed slats).

Additional fan
Due to the location of the condenser, in front of the radiator, the amount of air
passage is consequently reduced. By subjecting the engine to very high
stresses, with high external temperatures, this can lead to an unacceptable
increase in the temperature in the engine cooling system and in the coolant
circuit, thereby excessively increasing the pressure.

Therefore, to assist in the cooling of the engine and the air conditioning system,
an additional electric fan is arranged in front of the condenser, which is
connected or disconnected by a temperature switch on the radiator and/or by
the switch of the additional fan itself. on the rear side of the compressor.

In vehicles equipped with the extra equipment for "very hot countries", an
additional 2-speed fan is used, the first speed of which always operates as soon
as the air conditioning system is switched on.

Cooling liquid temperature switch

The coolant switch is mounted on the left side of the radiator.

To avoid excessive temperatures in the cooling liquid, this switch activates the
additional fan if the liquid temperature reaches approx. 105° C. and disconnects
it again at approximately 100° C.

Additional fan switch

The additional fan switch is located on the rear side of the compressor.
To avoid excessively high pressures in the coolant circuit, this switch switches
on the additional fan when a pressure of approx. 1800 to 2100 kPa and
disconnects it at approximately 1450 kPa.

Motronic switch

The Motronic switch (the name Motronic comes from gasoline injection systems
that use electronic management from BOSCH called "Motronic") is located in
the high-pressure liquid pipe between the condenser and the evaporator.

This switch causes an increase in the idle speed or prevents it by opening the
contacts, if the pressure in the coolant circuit reaches approx. 100±100kPa.

Low pressure safety switch

The low pressure safety switch is located next to the high pressure service
connection, in the high pressure liquid pipe between the condenser and the
evaporator, and serves to protect the air conditioning installation in the event
that insufficient amount of cooling agent.
This switch switches off the compressor as soon as the pressure in the air
conditioning system has dropped to 215 ± kPa.

As a general rule, the cause of the pressure dropping is due to an insufficient

amount of cooling agent or leaks in its circuit. Therefore, the low pressure
safety switch does not automatically switch the compressor back on. As not
only the refrigerant agent but also its oil can escape through leaks,
disconnecting the compressor is a safety measure to prevent it from breaking
down due to a lack of oil.

Dosing valve

The dosing valve is located in the intermediate piece of the high-pressure liquid
pipe between the condenser and the evaporator.

Through its invariably calibrated bore, this valve determines the passage of the
cooling agent through the system. Its mission is described in detail in the
section "Description of the coolant circuit".
Evaporator

The evaporator is located in the air distribution box.

The evaporator cools, dries and cleans the air that enters the passenger
compartment. With the air conditioning installation connected, the air that
passes between the lamellae of the evaporator core is cooled, condensing the
humidity in the air. Upon contact with the wet surfaces of the evaporator,
particles of dust, pollen, etc., are retained and, together with the condensed
water, conveyed to the outside through the flexible evacuation tubes arranged
under the distribution box. from air. The absolute humidity in the cabin is low,
which reduces fogging of the windows when driving in rainy, humid or cold
weather.

The evaporator is a heat exchanger whose function is inseparable from that of

the thermostatic expansion valve (reducing or dosing valve). During
evaporation, the refrigerant fluid absorbs the energy of the air driven by the
ventilation turbine in the vehicle's cabin, which is cooled by passing through the
evaporator pipes.

The temperature of the cooling agent in the evaporator is regulated so that the
humidity that occurs cannot freeze the surface of the evaporator core, which
would block the passage of air. Anti-freeze control is carried out by the control
valve on the compressor. As soon as the lowest admissible refrigerant
temperature has been reached in the evaporator; That is to say, a certain
pressure in it, without the evaporator yet freezing, the compressor regulates the
displacement, reducing the amount of refrigerant agent to the evaporator.
As said at the end of the first part of the course, the refrigerant agent R-12
(Freon 12) was replaced by the new R-134a, which in turn was accompanied by
other important changes in the constitution of the air conditioning system.
These changes were:

* Change of the R-12 refrigerant agent to R-134a (less harmful to the ozone
layer), free of hydrocarbon fluorochlorine.

* A thermostatically controlled expansion valve (TXV), with variable section,

replaces the stop valve (orifice valve), with calibrated section. The expansion
valve is located in the air distribution box.

* The dryer is mounted on the liquid pipe at the outlet of the condenser.

* Synthetic polyglycoalkylene oil is used as lubricant for the compressor instead

of mineral oil.

* Flexible tubes and pipes of different materials, as well as joints of modified

sizes.

* Modified toroidal seal rings.

* Filling amount of cooling agent.

* Slightly higher pressures in the cooling agent circuit.

* The high and low pressure safety switch is no longer located on the
compressor, but directly on the refrigerant pipe.

A new mobile service station and a new leak detection device are required for
service work.

The refrigerant and components of R-134a and R-12 systems should not be
interchanged. Mixing cooling agents with the components of both systems leads
to incorrect operation and deterioration of air conditioner parts.
Compressor

As we mentioned previously, the compressor no longer has the high and low
pressure safety switch. If we disassemble the compressor, do not leave the
connections open to prevent dirt and moisture from entering.

The overpressure valve has a marking attached to it. When this mark is missing,
it is a sign that refrigerant has already come out through the valve.

Service work on the compressor is limited to replacement of the control valve,

overpressure valve and pulley/magnetic coupling assembly. When assembling
the assembly, the size of the groove (1) between the pulley and the magnetic
coupling must be taken into account.
Compressor lubricant

The compressor lubricant is a synthetic polyglycoalkylene oil (PAG*), specially

designed to be applied with the R-134a refrigerant agent. This special oil
circulates together with the cooling agent through the entire cooling agent
circuit.

The mineral oil used until now and the new synthetic compressor lubricant
cannot be replaced or mixed with each other!

Before the first start-up of the air conditioner, all the lubricant (about 300 ml) is
in the compressor.

When emptying the air conditioner, a certain amount of lubricant also comes out
of the compressor. The same occurs when replacing a component of the coolant
circuit. The part of the compressor lubricant that comes out when the air
conditioner is emptied is collected at the mobile service station. When replacing
components of the refrigerant circuit it is necessary to measure the amount of
compressor lubricant remaining in the replaced component.

The total amount of compressor lubricant to be refilled is made up of the part

that remained in the replaced component and the part that came out when the
air conditioner was drained. Large deviations in the total amount of compressor
lubricant can lead to reduced performance of the air conditioner (too much
compressor lubricant) or damage to the compressor (insufficient or excessive
amount of compressor lubricant).

Compressor lubricant is filled into the component in question before assembly.

A new compressor comes filled with the amount of lubricant necessary for the
entire refrigeration circuit. If the compressor is replaced, it is necessary to first
measure the amount of lubricant in the old compressor. The lubricant from the
new compressor is emptied into a clean container. The new compressor is then
filled with the amount of filling from the old compressor.

Compressor lubricant is not consumed during operation of the air conditioner

and does not need to be replaced.

*P = Polyalkylene glycol

Thermostatic expansion valve (TXV)

The expansion valve is the separation point between the high and low pressure
zones in the refrigerant circuit and replaces the previously known shut-off valve
in the air conditioner.

The pressure drop after the expansion valve causes the evaporation of the
cooling agent.
The expansion valve is located in the air distribution casing between the inlet
and outlet pipes of the evaporator.

Contrary to the passage valve, which has a calibrated passage, the

thermostatic expansion valve is variable in its passage.

Functioning

The thermostatic expansion valve narrows the section of the refrigerant pipe.
The resulting drop in pressure causes the cooling agent to evaporate. The valve
is arranged between the inlet pipe (1) and outlet pipe of the evaporator (2).

The thermostatic expansion valve is a variable regulation element.

The size of the section is regulated by a thermostat. The thermostat controls

the temperature at which the refrigerant leaves the evaporator. A variation in
temperature causes the valve needle to move and, with it, the section of the
valve to change.

Switches

Triple switch
The triple switch contains:

* Low pressure safety switch

* High pressure safety switch

* Additional fan switch

The switch reacts to 3 different pressures in the high-pressure line and

connects the corresponding connection circuit.

The triple switch is mounted on the high pressure pipe, between the compressor
and the condenser.

The low pressure safety switch disconnects the magnetic coupling of the
compressor as soon as the pressure in the refrigerant circuit drops.

The high pressure safety switch disconnects the magnetic coupling of the
compressor as soon as the pressure in the refrigerant circuit exceeds
approximately 3000 kPa (30 bar). The high pressure safety switch switches the
compressor back on when the pressure drops below

from the normal value of about 2000 kPa (20 bar).

The auxiliary fan switch switches the auxiliary fan and the radiator fan from
speed 1 to speed 2 if the pressure is greater than about 1900 kPa (19 bar). When
the pressure drops below about 1500 kPa (15 bar), it switches back to speed 1.

Motronic switch (idle increase switch)

The Motronic switch raises the idle speed if the pressure in the coolant circuit
is around 1100 kPa (11 bar). At around 900 kPa (9 bar) the Motronic switch is
disconnected again.

The switch is located in the high pressure pipe, between the compressor and
the condenser.

Cooling liquid temperature switch

There are 2 temperature switches for the coolant on the engine radiator.

Switch 1 on the bottom of the radiator is the radiator fan switch. This switch
connects the radiator fan and the additional fan in series when the coolant
temperature reaches 100 °C. At 95 °C, disconnect the radiator fans again and.

additional.

Switch 2 located in the upper half of the engine radiator is a switch with 2
contacts. At 105 °C, one of the contacts connects the additional fan and the
radiator fan at speed 2. At 100 °C, turn the fan back on to speed 1. The other
contact disconnects the magnetic coupling

of the compressor at 120 °C and turns it on again at 115 °C.

Service Connections or Fill Valves

The function of the valves is:

* Authorize the connection of the fittings of the charging installation in the
refrigeration circuit,

* Ensure the opening of the circuit to carry out vacuum drag to eliminate air and
humidity and carry out filling or emptying,

* Guarantee the tightness of these loading points during the operation of the
refrigeration system.

They are made up of a body that contains a valve mechanism and a plug.

The valve ensures the closing of the loading point by the action of a spring.
When connecting the charging installation, the fitting acts on a pusher that
compresses the spring and releases the circuit opening. When connecting and
disconnecting, the action is carried out in such a way that the refrigeration
circuit never comes into contact with air

abroad.

These are two filling valves: one located in the high pressure part of the circuit,
between the condenser and the expansion valve, and another in the low
pressure part, between the evaporator and the compressor. This position of the
valves allows a homogeneous distribution of the fluid within the refrigeration
circuit, since the expansion valve and certain compressor valves can be closed
at the time of filling. Its location is precise to facilitate access when connecting
the fittings of the charging installation. In this way, they can be screwed inside
the body or inside the cylinder head of the compressor (corresponding to the
low pressure and high pressure chambers) or welded to the metal connecting
tubes.

The screw diameters with the refrigerant circuit filling tubes differ depending on
the refrigerant fluids used, HFC 134a (R-134a) or CFC 12 (R-12), to avoid any
loading error.

These valves are also used to place the pressure switches in the circuit: they
allow disassembly without causing fluid losses.

Checking the tightness of the refrigeration circuit

Filling is not effective if the refrigeration circuit is not perfectly sealed.

The tightness check is carried out when filling has finished and after putting the
circuit under pressure. Maintaining the vacuum, as a control of tightness, is only
a remedy to get out of trouble due to the reversal of the working direction of the
joints.

Systems for detecting losses in refrigeration circuits that use CFC 12 are
numerous but their effectiveness is not always complete:

* Protect the parts to be checked with soapy water or with a pump. However,
this method is inaccurate for small losses and for observing places less
accessible to the eye.

* Use a haloid lamp; However, working with it on the vehicle is dangerous due
to its flame.

* Add a dye to the fluid that leaves a visible trace at the site of the leak (Dytel
or similar, although this chemical is not accepted by compressor
manufacturers).

* Use an electronic leak detector. Although more expensive, these devices are
the most used by builders due to their effectiveness. Its precision is of the order
of 1 to 5 g. of fluid loss per year. An audible signal indicates the presence of
halogen fluid.

In circuits that use R 134a refrigeration fluid, losses are detected by the
Spectroline device.

This is a UV detection lamp. A fluorescent additive is previously added to the

refrigerant fluid. During the examination with the UV lamp, the losses transform
into a bright, fluorescent, greenish-yellow trace that precisely indicates the
origin of the loss.
Safety instructions

When dealing with cooling agents, protective glasses and gloves should always
be worn.

Prevent air conditioner parts from being exposed to heat:

* Vehicles equipped with air conditioning should not be subjected to 80°C in the
drying oven for more than 20 minutes. If this is necessary, the air conditioning
installation must then be emptied.

* When dewaxing or cleaning the engine, do not direct the steam jet directly at
the air conditioner parts.

The workplace where the refrigerant circuit is operated must always be well
ventilated.
Breathing in concentrations of the gasified cooling agent causes dizziness and
an impression of suffocation.

Do not work on the coolant circuit from an assembly pit. The gasified cooling
agent weighs more than air and can concentrate in large quantities in such pits.

When removing the flexible service hoses, do not bring the quick releases closer
to the body as some cooling agent could still escape from them.
End of the car air conditioning course