GMC 1986 P-Truck Service Manual page 76

INSUFFICIENT COOLING DIAGNOSIS CHART (CONTINUED)
FOAMING
SYSTEM IS PROBABLY LOW ON REFRIGERANT. CHECK
FOR LEAKS, REPAIR, AND ADD REFRIGERANT. IF FOAMING
STILL OCCURS, CHECK FOR RESTRICTION IN REFRIGERANT
SYSTEM BETWEEN CONDENSER AND SIGHT GLASS.
LOW EVAPORATOR
PRESSURE
REFER TO FIGURE 8
CHECK EVAPORATOR OUTLET LINE
EVAPORATOR OUTLET
LINE W ARM
CHECK FOR LIQUID LINE RESTRICTION (FROST SPOT
ON LINE). IF NOT,
CHECK FOR PLUGGED INLET SCREEN IN EXPANSION
VALVE. IF NOT,
3. CHECK FOR MALFUNCTIONING EXPANSION VALVE BY
REMOVING VALVE AND BLOWING THROUGH VALVE.
IF UNABLE TO BLOW THROUGH VALVE, BULB IS DIS­
CHARGED. REPLACE EXPANSION VALVE.
LOW DISCHARGE
PRESSURE
REFER TO
FIGURE 8
CHECK FOR MALFUNCTIONING EXPANSION VALVE.
Figure 14—Insufficient Cooling Diagnosis Chart (Cont.)
D A S H M O U N T E D U N IT (M O TO R H O M E C H ASS IS U N ITS )
DISCHARGE PRESSURE DROPS
AIR CONDITIONING
NO FOAMING
SYSTEM MAY BE EITHER FULLY CHARGED OR
EMPTY. FEEL HIGH AND LOWER PRESSURE PIPES AT
COMPRESSOR. HIGH PRESSURE PIPE SHOULD BE
WARM. LOW PRESSURE PIPES SHOULD BE COLD
IF PIPES ARE NOT INDICATING PROPER
TEMPERATURES, RECHARGE SYSTEM AS
RECOMMENDED. IF NOZZLE AIR TEMPERATURE IS
STILL HIGH, CHECK EVAPORATOR PRESSURE.
CHECK EVAPORATOR PRESSURE
REFER TO FIGURE 8
HIGH EVAPORATOR
PRESSURE
CHECK COMPRESSOR DISCHARGE PRESSURE
HIGH DISCHARGE PRESSURE
1. CHECK ENGINE COOLING SYSTEM, FAN CLUTCH AND
CHECK FOR RESTRICTED AIR FLOW THROUGH
CONDENSER.
2. CHECK EXPANSION VALVE BULB CONTACT. CORRECT
IF NECESSARY.
3. CHECK FOR REFRIGERANT RESTRICTION IN
CONDENSER. RETURN BENDS AT EQUAL ELEVATION
SHOULD BE APPROXIMATELY SAME TEMPERATURE.
IF TEMPERATURE OF BENDS IS APPRECIABLY
DIFFERENT, THE COOLER BEND INDICATES A
RESTRICTED CIRCUIT, REPLACE CONDENSER IF
RESTRICTION IS FOUND. IF CONDENSER IS GOOD,
CHECK FOR AIR IN SYSTEM. TO CHECK OBSERVE
OUTLET AIR TEMPERATURE AND COMPRESSOR
DISCHARGE PRESSURE WHILE SLOWLY DISCHARGING
SYSTEM AT RECEIVER INLET CONNECTION.
OUTLET AIR TEMPERATURE
DROPS AS COMPRESSOR
LEAK TEST SYSTEM, REPAIR
AS NECESSARY. DISCHARGE,
EVACUATE, AND RECHARGE.
1B-13
OUTLET AIR TEMPERATURE
INCREASES AS COMPRESSOR
DISCHARGE PRESSURE DROPS
REPLACE EXPANSION VALVE
F-00165