Chevrolet 1977 light duty truck Service Manual page 66

The following procedures should be applied before performance testing an A/C System.
1. Check for proper belt installation and tension w ith J-23600.
2. Check for proper clutch coil terminal connector installation.
3. Check for clutch air Gap (.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) 1
DISCHARGE TEMPERATURE
AT OUTLET COLD
CHECK FOR AIR LEAKS THROUGH DASH PANEL.
DOORS, WINDOWS, OR FROM HEATER.
( ! "
f o a m in g
SYSTEM IS PROBABLY LOW ON REFRIGERANT.
CHECK FOR LEAKS, REPAIR, AND ADD
REFRIGERANT. IF FOAMING S TILL OCCURS,
CHECK FOR RESTRICTION IN REFRIGERANT
SYSTEM BETWEEN CONDENSER AND SIGHT
GLASS.
o
LOW EVAPORATOR
•PRESSURE
CHECK EVAPORATOR OUTLET LINE
EVAPORATOR OUTLET
LINE WARM
1. CHECK FOR LIQ UID LINE RESTRICTION
(FROST SPOT ON LINE). IF NOT,
2. CHECK FOR PLUGGED INLET SCREEN IN
EXPANSION VALVE. IF NOT,
3. CHECK FOR DEFECTIVE EXPANSION VALV E
BY REMOVING VALVE AND BLOWING THROUGH
V ALV E. IF U N A B IF TO RLOW THROUGH V ALV E.
BULB IS DISCHARGED. REPLACE EXPANSION
V ALVE.
LOW DISCHARGE
* PRESSURE
Check fo r malfunctioning
expansion valve-See
Component Diagnosis.
•REFER TO PERFORMANCE
CHART FOR CORRECT PRESSURES
INSUFFICIENT COOLING D IA GNO SIS CHART (EXCEPT C-K FOUR-SEASON SYSTEM)
\
I NORMAL AIR FLOW
I
CHECK FOR BLOWN FUSE, DEFECTIVE BLOWER SWITCH,
HIGH OUTLET AIR
BROKEN WIRE, LOOSE CONNECTIONS, LOOSE BLOWER MOTOR
TEMPERATURE
GROUND WIRE OR INOPERATIVE BLOWER MOTOR.
CHECK SIGHT GLASS
NO FOAMING
, SYSTEM MAY BE EITHER FU LLY CHARGED OR FMPTY.
FEEL HIGH AND LOW 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.
~T~
' CHECK EVAPORATOR PRESSURE!
HIGH EVAPORATOR
* PRESSURE
CHECK COMPRESSOR DISCHARGE PRESSURE
* | HIGH DISCHARGE PRESSURE |
1. Check engine cooling system, fan clutch and check
for restricted air flow thru condenser.
2. Check expansion valve bulb contact.
necessary.
3. Check tor refrigerant restriction in condenser.
Return bends at equal elevation should be
approximately same 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.
air temperature and compressor discharge
pressure while slowly discharging system at
receiver inlet connection.
OUTLET AIR TEMPERATURE
DROPS AS COMPRESSOR
DISCHARGE PRESSURE DROPS
LEAK TEST SYSTEM, REPAIR
AS NECESSARY, DISCHARGE,
EVACUATE, AND RECHARGE.
5. Check fo r condenser air blockage due to foreign material.
6. Check fo r proper air ducting hose connections.
7. Check heater temperature dour adjustment, adjust if incorrect.
8. Check evaporator sealing fo r air leak, repair if leaking.
9. Install pressure gages and thermometer and make performance test.
- IN O OR LOW AIR FLOW I
CHECK AIR FLOW
1
CHECK BLOWER OPERATION
OWER NOT OPERATING
1 _______
SYSTEM HAS EXCESS MOISTURE. REPLACE RECEIVER
UEHYDRATOR AND EVACUATE THOROUGHLY. RECHARGE
SYSTEM.
EVAPORATOR PRESSURE
| Check Compressor Discharge Pressure. I
| LOW DISCHARGE PRESSURE
Check for restriction in liquid line,
partially plugged inlet screen at
Correct if
expansion valve, or defective
expansion valve, replace valve if
defective.
If temperature
To check observe outlet
OUTLET AIR TEMPERATURE
INCREASES AS COMPRESSOR
DISCHARGE PRESSURE DROPS
i ...............
REPLACE EXPANSION VALVE
i :___
JORMAL BLOWER OPERATION |
Check fo r 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.
ICE BLOCKING
EVAPORATOR
CHECK FOR LOW EVAPORATOR PRESSURE
1. ALLOW SYSTEM TO WARM UP.
2. S10P ANU RESTART ENGINE.
3. CHECK EVAPORATOR PRESSURE
IM M EDIATELY AFTER RESTART AND
PULL DOWN OF EVAPORATOR PRESSURE.
NORMAL EVAPORATOR LOW EVAPORATOR
* PRESSURE
PRESSURE
Check fo r malfunctioning
expansion valve-See
Component Diagnosis.
NORMAL
\
- I NORMAL DISCHARGE PRESSURE I
r _ _ .
i ' —
Refrigeration System is ok
1. Check for proper function of heater TEMPERATURE door.
L
Check fo r proper sealing of evaporator case.
3. Check fo r 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 see "CHECKING COMPRESSOR OIL CHARGE".
NOTE: G-MODELS, Insufficient cooling, or too much cooling may
be the result of a potentiometer out of calibration; see "A m p lifier
Board Potentiometer Adjustm ent" in the Maintenance and Adjust­
ment portion of this section.
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