Diagnosis; Testing The Refrigerant System; Leak Testing The Refrigerant System; Pressure Sensing Switch - GMC 1986 P-Truck Service Manual

NOTICE: When performing air conditioning di­
agnosis on vehicles equipped with a catalytic
converter, warm the engine to a normal oper­
ating temperature before attempting to idle
the engine for periods greater than five (5)
minutes. Make adjustments after the choke is
open and fast idle speed is reduced to a nor­
mal idle.
TESTING THE
REFRIGERANT SYSTEM
If a malfuction is suspected due to abnormal system
pressures, check the following:
1. Outer radiator and condensor cores for plugging.
Check between the condenser and radiator.
2. R estrictions or kinks in evaporator core or
condensor core, hoses, tubes, etc.
3. Refrigerant leaks.
4. Air ducts for leaks or restrictions. Air restriction
may indicate a plugged (or partially plugged)
evaporator core.
5. Compressor clutch slippage.
6. Improper drive belt tension.
7. Plugged accumulator, orifice (expansion tube) or
plugged suction inlet screen (A6 compressor).
8. Moisture in the refrigerant system.
LEAK TESTING THE
REFRIGERANT SYSTEM
Liquid Leak Detectors
Check for leaks at fittings and valves with the swab
attached to the bottle cap. Bubbles will form if there is
a leak.
For restricted areas, use a leak detector, J-6084 or
equivalent.
J-6085 LEAK DETECTOR
Tool J-6084 is a propane gas-burning torch used to
locate refrigerant leaks. Refrigerant gas drawn into the
sampling tube attached to the torch will cause the
torch flame to change color in proportion to the size of
the leak. Propane gas fuel cylinders used with the
torch are available commercially.
CAUTION: Do not use a lighted detector
where c o m b u s tib le or e xp lo s iv e gasses,
dusts or vapors may be present.

DIAGNOSIS

Operating Detector
1. Determine if there is sufficient refrigerant in the
sytem for leak testing.
CAUTION: Do not breathe the fumes that are
produced by the burning of Refrigerant-12
gas in the detector flame. These fumes can
be toxic in large concentrations.
2. Open control valve until a low hiss of gas is
heard; then light gas at opening in chimney.
3. Adjust until the blue flame is about 10mm (3/a-
inch) above the reactor plate. The reaction plate
will heat to a cherry red.
4. Explore for leaks by moving the end of the
sampling hose around possible leak points in the
system. Do not pinch or kink hose. Since
Refrigerant-12 is heavier than air, place open end
of sampling tube below point being tested.
5. Watch for color changes. Small leaks will turn the
flame to green or yellow-green; large leaks will
turn the flame a brilliant blue or purple. After
passing through a leak the flame will turn to a
c o lo rle s s
semi-darkened area. If the flame remains yellow
after removing it from a leak, the reaction plate is
dirty or the flame is drawing insufficient air.
To check a leak in the high pressure side of the
system, operate the system for a minute, shut down
and check. To check a leak on the low pressure, op­
erate the system and check several minutes after
turning off the system. This will equalize both sides.

PRESSURE SENSING SWITCH

A pressure sensing switch located near the top of
the accumulator, cycles the compressor clutch on C-K
and G series CCOT A/C systems. The switch also
shuts off the compressor clutch when there is a low
refrigerant charge.
The A/C system does not have to be discharged to
replace the switch. The pressure switch fitting is
equipped with a schrader-type valve.
When replacing the switch, use a new oiled seal
(o-ring), and torque to 10 N m (90 in. lbs.).
Refer to the following trouble shooting charts-
1. Pressure C ycling CCOT System Diagnosis
(figures 11 and 12).
2. System Diagnosis (Dash Mounted Unit) (figures
13, 14 and 15).
3. Compressor Diagnosis (figure 16).
AIR CONDITIONING 1B-9
pale b lu e . Make te s ts in a