Page 771
AIR CONDITIONING SYSTEM
The air conditioning system is designed to control the
temperature, humidity, purity and circulation of air. The
system cools and dries the air in the passengercompartment.
1
5
3
4
S 5557
AIR CONDITIONING
SYSTEM
1. Compressor
2. Condenser
3. Receiver/Drier
4. Expansion valve
5. Evaporator
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854-6
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Page 772
FUNCTIONAL DESCRIPTION
The main components in the mechanical system are the
evaporator, compressor, condenser, receiver and
expansion valve.
A special refrigerant ( R 12) absorbs heat inside the evaporator by changing from a liquid to a vapour. The evaporator is located inside the passenger compartment. The air
flows over the fins of the evaporator and, having been
cooled, is directed into the passenger compartment.
-The temperature of the evaporator should be as low as
possible without ice forming on its surface.
The temperature of the refrigerant may be several degrees lower than that of the air passing through the evaporator owing to the temperature rise through the walls
of the cooling fins and coils. The latter is sufficient to
prevent the formation of ice.
The compressor pressurizes the heat-laden vapour until
its temperature is considerably higher than the outside
air. The vapour is then pumped to the condenser, where
it gives up its heat and changes once again to a liquid.
The compressor and condenser are located in the engine
compartment. On its way to the evaporator, the refrigerant
passes through the receiver where it is filtered and dried.
The refrigerant in the form of gas in the condenser gives
off heat which is carried off by air flowing over the condenser fins.
The refrigerant then changes state from a gas to a liquid
(condenses). The liquid refrigerant is then filtered, dried
and stored under pressure in the receiver for subsequent
supply to the evaporator. The flow of refrigerant from
the receiver to the evaporator is regulated by the thermostatic expansion valve. The expansion valve reduces
the presslfe, whereupon the refrigerant starts to boil i.e. vaporize. At this point, the refrigerant absorbs heat
from the air passing over the fins of the evaporator. By
means of the compressor, the heat is transferred to the
condenser where it is carried off by air flowing through
the condenser fins.
4
SKETCH OF FUNCTION
1. Evaporator
2. Compressor
3. Condenser
4. Reciever
5. Expansion valve
l
854-7
■
Liquid
~
Mixture of gas and liquid
[T'.@I
Vapour
Page 773
Refrigerant
The refrigerant used in the system is R 12 which is one of
the safest refrigerants available. It is capable of withstanding high pressures and high temperatures without deteriorating or decomposing.
However, it can form a poisonous gas (phosgene) if allowed to come into contact with an open flame or very hot
metal.
Safety precautions
R 12 is odourless and cannot be detected in small quantities. It is colourless and will not stain.
Suitable eye protection should be worn when R 12 is to
be handled owing to its low vaporization temperature.
At atmosperic pressure, R 12 vaporizes at -22°F (-30°C).
If liquid R12 enters the eye, the eyeball may freeze. If
an eye freezes, it may cause blindness. If the liquid enters
the eye, follow these instructions:
1. Do not rub the eye.
2. Splash large quantities of cool water into the eye to
raise the temperature.
3. Apply clean petroleum jelly to the eye to help prevent
infection.
4. Tape on an eye patch to prevent dirt entering the eye.
5. Without delay, visit a doctor or hospital as fast as possible.
6. Do not attempt to treat it yourself.
Frostbite may occur if R 12 comes into contact with the
skin. Always exercise great care when handling the refrigerant. If it should come into contact with any other
part of the body, follow the same procedure as outlined
above.
R 12 is otherwise harmless unless released in a confined
space, when it may cause drowsiness. However, the volume used in car air conditioning systems is not sufficient
to give rise to any problems.
If R 12 is allowed to come into contact withan open
flame or very hot metal, phosgene gas will be formed.
This gas is poisonous and potentially very dangerous. A
person inhaling the gas can become very sick. Small
quantities of phosgene gas inhaled over a period of time
can accumulate in the body and may result in a toxic
condition. Consequently, the greatest care should be taken
when propane torch leak detectors are used. Always ensure that the premises are well ventilated and that the air
circulation is good.
The following rules must be observed when R 12 is being
handled:
1. Above 129°F (54°C), liquid refrigerant will completely fill a container and hydrostatic pressure will build
up rapidly with temperature rise. For this reason, never heat a container above 122°F (50°C).
2. Never apply an open flame to a refrigerant container
Never place an electric resistance heater near to, or in
direct contact with, a container.
3. Never handle a container carelessly. To avoid damage,
always use an approved spanner or wrench to open
and close the valves. Secure the containers in an upright position for storage and transport of the refrigerant.
4. Never handle the refrigerant without suitable eye protection.
5. Never overheat the container.
6. Never discharge refrigerant into an enclosed area where
there is an open flame.
7. Always discharge the refrigerant slowly when draining
•the system.
8. Do not introduce anything but pure R 12 and a refrigerant oil into the system.
9. · Never touch a damp container with bare hands while
a system is being charged. The hand may become frozen to the container. Should this happen, pour water
onto the container to thaw and thereby free the hand.
Refrigerant oil
A small quantity of oil is circulated through the system
with the refrigerant to lubricate the seals, gaskets and
other moving parts of the compressor. The oil is necessary
for keeping the thermostatic expansion valve in proper
operating condition owing to the close design tolerances
of the valve. Only non-foaming oil, with a viscosity of
500 SUS at 100°F (+38°C), specially designed for use in
air conditioning systems should be used.
854-8
Page 774
1
SYSTEM COMPONENTS
The following describes the circulation of the refrigerant
through the system and the function of the various components.
The receiver
The receiver is the part of the system in which the refrigerant is stored. It comprises a cylindrical metal container
with fittings for inlet and outlet, and a sight glass. It is located in the high-pressure side of the system and, for the
most part, contains liquid refrigerant. The receiver consists
of two sections, namely, the receiver section and the drier
section.
The receiver section accepts and stores the correct amount
of excess refrigerant that the system requires to operate
properly. It supplies a steady flow of liquid refrigerant to
the thermostatic expansion valve. The drier section contains a bag of desiccant (silica gel), that absorbs and holds
small quantities of moisture, and a filter, that collects particles that could otherwise affect the circulation in the
system. The drier section is equipped with a sight glass
which indicates whether there is sufficient refrigerant in
the system.
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f I el J
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f
0
S 5560
SIGHT GLASS
854-9
5
t
THE DRIER SECTION
1. Sight glass
2. From condenser
3. Filter
4. Pickup tube
5. To expansion valve
Clear sight glass - system correctly charged or overcharged
Occasional bubbles - refrigerant charge slightly low
Oil streaks on sight glass - total lack of refrigerant
Heavy stream of bubbles - serious shortage of refrigerant
Dark or clouded sight glass - contaminent present
Page 775
Thermostatic expansionvalve and evaporator
The thermostatic expansion valve is located at the inlet
side of the evaporator. The expansion valve controls the
system and serves to separate the low and high-pressure
side of the system. The valve orifice (0.008 in./0.2 mm
max.) only permits the passage of a small quantity of refrigerant. The evaporator temperature is regulated by
means of the quantity of refrigerant entering.
The state of the refrigerant inside, and immediately after,
the expansion valve is liquid, but, as soon as the pressure
drops, it starts to boii, absorbing the heat from the air
flowing over the fins on the evaporator. In other words,
heat is removed from the surrounding air.
The quantity of refrigerant admitted to the evaporator
must leave the latter as 100 % low-pressure vapour or gas.
If too much refrigerant is metered to the evaporator,
there will be no change of state from liquid to gas. Since
the refrigerant pressure will be higher, it will not boil,
since there is no space for vaporization. An excess of liquid refrigerant from the evaporator may also damage
the compressor.
If too little refrigerant is metered into the evaporator, the
system will be "starved". Again the unit will not cool.
The refrigerant will vaporize or boil off before it reaches
the evaporator. When a correct quantity of refrigerant is
metired, it will be 100 % liquid immediately after the expansion valve, and 100 % gas (low-pressure gas) at the
outlet or tailpipe. The low-pressure gas is then directed to
the compressor inlet. The expansion valve is equipped
with a capillary tube which monitors the outlet temperature and thus controls the flow of refrigerant.
2
3
A
4
B
S 5561
EXPANSION VALVE
1. Capillary tube
2. Diaphragm
3. From receiver
4. To evaporator
A = Open valve
B = Close valve
854-10
Page 776
7
The compressor
The compressor pressurizes the refrigerant and directs it
through the system. The pressure increase which occurs
in the compressor causes more rapid condensation of the
refrigerant in the condenser. The compressor is a 2-cylinder unit equipped with suction and discharge valves.
When the piston is on the down stroke, the pressure
above the suction valve forces it open, and the discharge
valve is closed. When the piston is on the up stroke, the
suction valve is closed by increased pressure in the cylin-
der, the discharge valve starts to open and high-pressure
gas is discharged into the system. While one piston is on
the up stroke, the other is on the down stroke. The compressor separates the low-pressure side and the high-pressure side of the system.
The refrigerant enters the compressor as low-pressure gas
and leaves as high-pressure gas. The compressor is equipped
with service valves, facilitating the connection of pressure
gauges, etc., during servicing of the air conditioning system.
5
2
.~
..,:~: ..
:;?:•1·
4
,...
1
6
S 5562
PISTON MOVEMENT
1. Piston on down stroke
2. Suction valve open
3. Discharge valve closed
4. Suction valve closed
5. Discharge valve open
6. Piston on up stroke.
COMPRESSOR WITH MAGNETIC
1. Compressor
2. Field coil
3. Retaining screw
4. Magnetic clutch, pulley
5. Washer
6. Screw
854-11
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CLUTCH
Page 777
The condenser
The condenser converts (condenses) the refrigerant in the
gas state to that of a liquid. To do so it must give up its
heat, which is carried off by the air flowing over the fins
of the condenser. This heat which is now removed to
cause a change of state from a gas to a liquid is the same
heat which was absorbed in the evaporator to cause a
change of state from a liquid to a gas, with the addition
of the heat due to the pressure increase caused by the
compressor.
3
CONDENSER
1. Copper tubing
2. Inlet
3. Outlet
SA-a
854-12
Page 778
The electrical system
The system is controlled from the instrument panel by
means of two switches: one for the fan motor of the system and one for temperature control. To actuate the system, both switches must be on. Through a capillary tube
from the evaporator, the thermostatic switch senses the
temperature in the tube and co£Jtrols the cutting in and
out of the compressor.
Cars with injection engines are equipped with a device for
increasing the idling speed. This supplies additional air to
the engine through the crankcase pipe by means of a valve
located in the inlet manifold on the engine, which opens
when the compressor cuts in and starts running. Two
switches are located on the receiver, a low-pressure and a
high-pressure switch. The low-pressure switch actuates
the car radiator fan when a preset pressure is reached in
the system. If the system pressure should become too
high, the high-pressure switch will break the circuit to
the magnetic clutch on the compressor. Power to the electrical system is supplied from the fuse box on the car
through a 30A fuse in a hanging fuse holder.
1
3
11
WIRING DIAGRAM
1. Solenoid valve "High Idle"
2. High-pressure switch
3. Thermostatic switch
4. Fan motor switch
5. Fan motor
6. Compressor clutch
7. 30A fuse
8. Thermostatic switch, radiator fan motor
9. Low-pressure switch
10. Fuse box
11. To radiator fan relay (cable 114)
854-13
:.
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Page 779
6.
Charging and discharging the system
Equipment: Portable servicing equipment comprising a
vacuum pump, low-pressure gauge (pressure 30 in. Hg to
+ 220 psi/1 kp/cm2 to + 15 kp/cm2), high-pressure gauge
(pressure range O psi to+ 500 psi/0 kp/cm2 to+ 35 kp/cm2),
scales (for weighing gas cylinder).
Gas (refrigerant): Cooling medium R12
Consumption:
1.76-1.87 lb. (0.80-0.85 kg).
7.
8.
9.
10.
Discharging the system
1. Connect the high-pressure hose from the manifold
gauge set to the high-pressure side of the compressor
(marked DISCH) and open the high-pressure valve.
2. Carefully open the middle valve on the manifold gauge
set and allow the refrigerant to discharge slowly. Rapid
discharge will force excessive oil out of the system
making it necessary to recharge the system with refrigerant oil.
N. B. If the system has been purged of refrigerant for any
length of time, the receiver unit should be replaced.
CAUTION
When charging and discharging the system, always
wear protective gloves and tightly fitting goggles to
avoid injury due to frost.
11.
12.
13.
14.
Connect the yellow hose to the vacuum pump.
Start the vacuum pump and open both valves. Let
the pump run for about thirty minutes.
Shut the valve and switch off the vacuum pump.
Connect the yellow hose to the gas cylinder. Purge
the hose as described in point 5a.
Open the valve on the gas cylinder and then the
low-pressure valve which should be adjusted so
that the reading on the low-pressure gauge will be
between +40 psi (2.8 and 3.0 kp/cm2).
Run the engine and adjust the speed to 1250 rev/
min. Short the radiator fan so that it runs contin·
ously. Set the system to maximum cooling and
maximum fan speed. Set the car heating system to
maximum heat and maximum fan speed, with only
the valve for the air supply to the front floor open.
Charge the system with 1. 76 lb. (0.8 kg) R 12 or until the sight glass is free from bubbles (clear liquid)
for between 10-15 seconds.
Shut the low-pressure valve and then the valve on
the gas cylinder.
Carefully disconnect the hose connections.
Connect the radiator fan for normal operation.
FAULT-TRACING
Inadequate cooling.
Blockage in the gas circuit.
Incorrect quantity of gas.
No cooling.
Compressor not running.
Fault in electrical system.
No cooling.
Compressor running.
Insufficient refrigerant in
system. Blockage in gas
circuit.
Adequate cooling immediately after start but deterioration after the system has operated for a
while.
Moisture in system.
Blockage in gas circuit.
Formation of ice in evaporator.
Magnetic clutch slipping.
Voltage drop. ( Refer to
section on changing the
magnetic clutch.)
Charging the system
1.
2.
3.
4.
5.
Connect the low- and high-pressure hoses to the
compressor and the yellow hose to the vacuum
pump.
Start the vacuum pump.
Open both valves on the manifold gauge set and
let the vacuum pump run for about 5 minutes.
Close the valve and switch off the vacuum pump
after the low pressure gauge has indicated 29 in.
Hg (0.95 kp/cm2). The vacuum on the low pressure
side should now not drop by more than 1 in. Hg
(0.05 kp/cm2)/five minutes if the system is tight.
Test for blockages in the system.
a. Connect the yellow hose (central manifold line)
to the gas cylinder. Loosen slightly the yellow
hose connection at the manifold gauge set and
purge the line of air by means of the gas cylinder (both valves closed).
b. Open the valve on the gas cylinder and the lowpressure valve on the manifold gauge set. If the
system is free of blockages, both the high-pressure and low-pressure readings will increase.
c. Shut the low-pressure valve and the valve on the
gas cylinder.
d. Release any excess pressure in the system.
SAAB
854-14
Page 780
Check the functioning of the high-and low-pressure
switches
(N.B. Both switches operate on the high-pressure side.)
TESTING
Checking the pressure
Connect the manifold gauge set (see section on charging
and discharging the system).
Testing by driving car
The normal readings when the car is being driven at 56
miles/h (90 km/h) and with an outside temperature of
between 68 and 95°F (20 and 35°C) is 1-1.5 kp/cm2
for the low-pressure side and 13-18 kp/cm2 for the highpressure side.
Workshoptesting
A. Idling
At normal idling speed and with the system set to maximum, the high-pressure level should be between 15 and
18 kp/cm 2 at room temperature. The level on the lowpressure side may vary between 1.5 and 2.5 kp/cm 2 . It is
normal to observe bubbles in the sight glass.
B. 2500 rev/min
The pressure on the high-pressure side should normally
be between 15 and 18 kp/cm2, and between 0.9 and 1.5
kp/cm2 on the low-pressure side. No bubbles should be
observed in the sight glass.
Possible causes of excessive pressure on high-pressure
side:
1. Excessive refrigerant in system.
2. Condenser clogged by external contaminants.
• 3. Defective operation of radiator fan.
Possible causes of insufficient pressure on high-pressure
side:
1. Insufficient refrigerant in system.
2. Blockage in gas circuit.
Possible causes of excessive pressure on low-pressure side:
1. Defective compressor (valve).
2. Defective expansion valve.
3. Defective refrigerant.
Possible causes of insufficient pressure on low-pressure
side:
1. Thermostatic switch not functioning. (Check that the
capillary tube is correctly fitted in the evaporator.)
2. Moisture in gas circuit (formation of ice in thermostatic valve).
3. Incorrect _quantity of refrigerant.
854-15
The high-pressure switch (actuation range 21-25 kp/cm2)
is closed when non-pressurized and is electrically connected in series with the magnetic clutch on the compressor. If the pressure on the high-pressure side reaches 25
kp/cm 2 (21 kp/cm 2 in earlier versions) the circuit to the
magnetic clutch on the compressor will be broken. When
the pressure has fallen by between 3 and 6 kp/cm2, the
circuit will again be closed.
To test the functioning of the switch, run the engine at
idling speed, set the system to maximum and temporarily
isolate the radiator fan. (Check that the engine temperature does not become too high.)
The low-pressure switch is largely a device to control the
car radiator fan which is an essential function if efficient
cooling is to be achieved.
The low-pressure switch is clos!rl when non-pressurized
and is electrically connected in parallel with the conventiona I thermostatic switch of the cooling system. The actuation range for the low-pressure switch is between 16
and 18 kp/cm 2 . When the pressure on the high-pressure
side is within this range, the radiator fan will cut in. When
the pressure has fallen by between 2 and 4 kp/cm2, the
radiator fan will cut out, unless the temperature of the
engine coolant is sufficiently high for the fan to be
switched on by the thermostatic switch.
The functioning of the switch can be checl<ed by running
the engine at idling speed with the air conditioning system set to maximum. No other action is necessary for
the check.
When check-readings of the values are made, ensure that
the pressure at the measuring points on the compressor is
approximately 1 kp/cm 2 higher than at the connectiC'n
of the switch in the receiver.
Belt tension
For satisfactory operation, the tension of the belt must
be maintained within the prescribed limits.
The most accurate way of checking the tension is by
means of a belt tension gauge.
When fitting a new belt, adjust the tension to 445 N
(44.5 kp) and at subsequent services to 355 N (35.5 kp).
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