Pontiac FIREBIRD 1972 Service Manual page 76

CUSTOM AIR CONDITIONING 1A-17
The system will have high pressure control more
frequently under this condition. Also see P.O.A.
VALVE INLET PRESSURE TOO HIGH
Overcharge of refrigerant or air in system.
Install gauge set and bleed off refrigerant from
(Note: Disconnect thermal limiter
P.O.A. valve suction side and compressor discharge
before discharging the system.)
side for 20 seconds. After 20 seconds close
valves and recheck pressures. Repeat until
discharge pressure is normal. Check sight glass.
If bubbles appear, it indicates that air was in
system. Charge as follows: 2000 engine rpm,
A/C mode, Hi blower and maximum cooling. Add
refrigerant until sight glass clears, then add
one-half pound additional.
Restriction in condenser, receiver-dehydrator or
Remove parts, inspect and clean or replace.
any high pressure line.
Condenser air flow blocked. Clean condenser.
P.O.A. Valve Inlet Pressure too high.
See P.O.A. Valve Inlet Pressure Too High.
COMPRESSOR DISCHARGE PRESSURE TOO LOW
CONDITION AND CAUSE
Insufficient refrigerant.
Defective Compressor.
Plug in refrigerant System.
P.O.A. Valve inlet pressure too low.
CORRECTION
Check sight glass for presence of bubbles or
foam. If bubbles or foam are noted, charge
as follows: 2000 engine rpm, A/C mode, Hi
blower and maximum cooling. Add refrigerant until
sight glass clears; add an additional 1/2 pound.
(It is not unusual for bubbling to occur on
minimum cooling and LO blower in mild weather even
with fully charged system.)
See Service Procedures-Compressor Assembly.
1. Disconnect fitting assembly and hoses from
compressor; disconnect receiver-dehydrator inlet
and outlet tube. Seal the compressor ports and
receiver fittings.
2. Check ends of lines for slipping plugs or torn-
off spare pieces of plugs left in at assembly.
3. Blow dry nitrogen, refrigerant or dry air
through lines to determine if lines or condenser
are plugged.
CAUTION: Bleed air hose of all moisture.
4. If plug in the system has not been found,
disconnect P.O.A. valve from evaporator.
5. Blow thru expansion valve and evaporator, to
check for plugged evaporator.
See P.O.A. Valve Inlet Pressure Too Low.
P.O.A. VALVE INLET PRESSURE TOO HIGH
CONDITION AND CAUSE CORRECTION
P.O.A. Valve stuck open.
Remove valve and inspect.
Expansion valve capillary tube to evaporator
CAUTION: Use only prescribed valve.
tube.
Remove insulation. Inspect for clearance between
tube and bulb. If gap exists, move bulb to
establish contact, reclamp and reinsulate.
Expansion valve inoperative.
Remove expansion valve and inspect screen for
foreign objects. If present, it is possible
seat is being held open. Install new expansion
valve; if condition is corrected, discard valve
removed.