GMC 1976 ZEO 6083 Maintenance Manual page 118

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DISCHARGE TEMPERATURE
AT OUTLET COLD
FOAMING
3
The following procedures should be applied before performance testing an A/C System .
1 . Check for proper belt installation and tension with J-23600.
2 . Check for proper clutch coil terminal connector installation.
3 . Check for clutch air Gap 1 .022 - .057) .
4 . Check for broken, burst, or cut hoses . Also check for loose fittings on all components.
CHECK DISCHARGE AIR TEMPERATURE (SEE PERFORMANCE DATA)
CHECK FOR AIR LEAKS THROUGH DASH PANEL.
DOORS, WINDOWS, OR FROM HEATER .
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
IF
CHECK EVAPORATOR OUTLET LINE
EVAPORATOR OUTLET
LINE WARM
1 . CHECK FOR LIQUID LINE RESTRICTION
(FROST SPOT ON LINE) . IF NOT,
2. CHECK FOR PLUGGED INLET SCREEN IN
EXPANSION VALVE . IF NOT,
CHECK FOR DEFECTIVE EXPANSION VALVE
BY REMOVING VALVE AND BLOWING THROUGH
VALVE . IF UNABLE TO BLOW THROUGH VALVE,
BULB IS DISCHARGED . REPLACE EXPANSION
VALVE .
LOW DISCHARGE
' PRESSURE
Check for malfunctioning
expansion valve-See
Component Diagnosis .
INSUFFICIENT COOLING DIAGNOSIS CHART
NORMAL AIR FLOW
HIGH OUTLET AIR
TEMPERATURE
1 . SYSTEM MAY BE EITHER FULLY CHARGED OR EMPTY .
FEEL HIGH AND LOW PRESSURE PIPES AT COMPRESSOR .
HIGH PRESSURE PIPE SHOULD BE WARM . LOW PRESSURE
PIPES SHOULD BE COLD .
2 . IF PIPES ARE NOT INDICATING PROPER TEMPERATURES,
RECHARGE SYSTEM AS RECOMMENDED . IF NOZZLE AIR
TEMPERATURE IS STILL HIGH . CHECK EVAPORATOR
PRESSURE .
CHECK EVAPORATOR PRESSURE
HIGH EVAPORATOR
'
PRESSURE
CHECK COMPRESSOR DISCHARGE PRESSURE
CHECK AIR FLOW
HIGH DISCHARGE PRESSURE
1 . Check engine cooling system, fan clutch and check
for restricted air flow thru 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 con-
denser if restriction is found, If condenser is OK,
check for air in system. To check observe outlet
air temperature and compressor discharge
pressure while slowly discharging system at
receiver inlet connection.
CHECK FOR BLOWN FUSE, DEFECTIVE BLOWER SWITCH,
BROKEN WIRE, LOOSE CONNECTIONS, LOOSE BLOWER MOTOR
GROUND WIRE OR INOPERATIVE BLOWER MOTOR .
OUTLET AIR TEMPERATURE
DROPS AS COMPRESSOR
DISCHARGE PRESSURE DROPS
LEAK TEST SYSTEM, REPAIR
AS NECESSARY, DISCHARGE,
EVACUATE, AND RECHARGE .
5. Check for condenser air blockage due to foreign material .
6. Check for proper air ducting hose connections .
7. Check heater temperature door adjustment, adjust if incorrect.
8. Check evaporator sealing for air leak, repair if leaking .
9. Install pressure gages and thermometer and make performance test .
BLOWER NOT OPERATING
LOW DISCHARGE
NO
SYSTEM HAS EXCESS MOISTURE. REPLACE RECEIVER
DEHYDRATOR AND EVACUATE THOROUGHLY. RECHARGE
SYSTEM-
PRESSURE
Check for restriction in liquid line
partially plugged inlet screen at
expansion valve, or defective
expansion valve, replace valve if
defective.
OUTLET AIR TEMPERATURE
INCREASES AS COMPRESSOR
DISCHARGE PRESSURE DROPS
REPLACE EXPANSION VALVE
OR LOW AIR FLOW
CHECK BLOWER OPERATION
NORMAL
EVAPORATOR PRESSURE
Check for loose or disconnected air distribution ducts,
restricted or leaking air ducts, partially closed air out-
let valve or clogged evaporator core, if above check is
OK, check for ice blocking evaporator .
NORMAL EVAPORATOR
'
PRESSURE
Check Compressor Discharge Pressure
NORMAL BLOWER OPERATION
ICE BLOCKING
EVAPORATOR
CHECK FOR LOW EVAPORATOR PRESSURE
1 . ALLOW SYSTEM TO WARM UP .
2. STOP AND RESTART ENGINE .
3. CHECK EVAPORATOR PRESSURE
IMMEDIATELY AFTER RESTART AND
PULL DOWN OF EVAPORATOR PRESSURE
NORMAL DISCHARGE PRESSURE
'REFER TO PERFORMANCE
CHART FOR CORRECT PRESSURES
LOW EVAPORATOR
' PRESSURE
Check for malfunctioning
expansion valve-See
Component Diagnosis .
Refrigeration System is ok
1 . Check for proper function of heater TEMPERATURE door .
2. Check for proper sealing of evaporator case.
3. Check for proper operation and seal around temperature door.
4 . Non-Foaming sight glass does not always indicate a fully
charged system . Add 1/2 lb . refrigerant and observe
performance .
5 . Check for excess oil in system. A symptom of excess oil is a
slipping clutch or belt or broken belt. To remove excess oil
in system consult service manual .
A-2317