Subaru XT 1988 Service Manual page 1034

4-7
AIR CONDITIONING SYSTEM
gas (phosgene gas) is produced when it contacts fire and
special care is therefore required when checking for leaks in
the system with a halide torch.
5) Do not steam clean on the system, especially condenser
since excessively high pressure will build up in the system,
resulting in explosion of the system.
The above precautions are essential in handling of Refrigerant-
12, and their strict observation requires sufficient training.
Therefore, it is of first importance that any other personnel
than a well-trained serviceman should not be allowed to handle
the retrigerant.
EVACUATING AND CHARGING SYSTEM
During servicing, use caution to keep air from getting into
refrigerant. When air enters the system, all refrigerant must
be evacuated from system prior to charging new refrigerant.
Air in refrigerant has the following deleterious effects:
1) Since the condensation temperature of the air is ex·
tremely low, the air will not be condensed when refrigerant
gas is condensed in the condenser, and the air will thus remain
in gaseous form. Consequently, the effective thermal trans·
mission area of condenser for refrigerant gas will be reduced
and refrigerant gas to be condensed· will be reduced. The
pressure rise will become proportional to the volume of the air
in system.
2) When air and refrigerant are mixed in system, a chemical
reaction will be produced and hydrochloric acid which will
adversely affect the aluminum, copper, iron, and other
materials in system may be generated.
Handling manifold gauge
The pressure at the high· and low-sides of system should be
measured when evacuating and charging refrigerant and
when diagnosing trouble in the system. The manifold gauge
is used for these purposes. A manifold gauge has two pressure
gauges; a low pressure gauge and a high pressure gauge.
These gauges are connected to the high· and low-side service
valves of system through flexible charging hoses. The con·
struction of manifold gauge is shown in Figure.
When valve stem is fully screwed, the valve is front·seated and
valve path and the center path are blocked. When valve stem is
backed off, the paths are opened.
Back-seated
(Full counter·
clockwise)
Fig. 8
To low-side To vacuum To high-side
. I pump or service valve
service va ve refrigerant can
A26-Q28
12
(Connection to service valve)
1) Fully close both valves of manifold gauge. Connect
high· and low-pressure charging hoses to manifold gauge.
2) Remove caps from service valves. Connect high· and low·
pressure charging hoses to service valves in system. The
refrigerant gas will be discharged since check valve is open
when pressing charging hose onto service valve.
3) Next, loosen the connection fitting of charging hose at
manifold gauge side for 2 to 3 seconds to purge any air inside
charging hose by the pressurized gas in system.
(Disconnection from service valve)
1) Fully close both valves of manifold gauge.
2) Disconnect two charging hoses from service valves. At
this time, the gas will be discharged until check valve is closed.
Therefore, disconnect hose quickly.
CAUTION:
When working with refrigerant, protect your fingers against
frostbite by using gloves or other cloth material.
Handling service valve
An automatic check valve is built into service valve. When this
valve presses against the connection fitting, that is, when
charging hose is connected to service valve. the valve is open.
When charging hose is disconnected, the valve is closed auto·
matically. Always observe the following usage precautions:
1) Always install valve cap after using service valve.
When high speed operation is performed without valve cap. a
negative pressure will gradually build up at the low pressure
side of system and air may be sucked in. In addition, dirt and
dust will easily enter the valve resulting in foreign matter
entering the system.
2) Check valve will be half opened during connection and
disconnection of charging hoses and refrigerant will be
forcefully discharged. Therefore, connect and disconnect
charging hoses quickly while pressing flare nut of charging
hose against service valve.
CAUTION:
When working with refrigerant, protect your fingers against
frostbite by using gloves or other cloth material.
3) Since close contact between the thread of valve cap and
the thread of service valve will prevent gas leakage, keep these
sections clean and free of scratches and damage.
4) Since packing of charging hose will be lost during long
use, always check packing prior to installing charging hose.