GMC 4000 Series Service Manual page 103

Sec. 1
Page 96
AIR CONDITIONING
Inspect system for visual de-
fe c ts. Check airt temperature.
HIGH AIR
TEMPERATURE
Check sight g la ss.
Check
leakage in air ducts, partially closed air
outlet valve or clogged evaporator core.
NO FOAMING
Check evaporator pressu re.
NORMAL
EVAPORATOR PRESSURE
C h ec k - com pressor
discharge p ressu re.
COMPRESSOR HIGH
DISCHARGE PRESSURE
Check for air in system , e x cess
refrigerant, restrictio n in con­
denser refrigerant tubes or air
fins. See Note "B."
COMPRESSOR LOW
DISCHARGE PRESSURE
Check for low refrigerant, r e s tr ic ­
tion in liquid line, plugged or de­
fective expansion valve, or defective
com pressor or
valve. See Note "C."
COMPRESSOR NORMAL
DISCHARGE PRESSURE
Check for proper seal around
evaporator core and tem per­
ature door.
G M C S E R V I C E M A N U A L
NORMAL AIR
TEMPERATURE
Check for air leaks at cab doors,
windows, cowl, or unit drain hose.
Check for blown fuse, defective blower
switch,
i
w ire, defective blower motor.
NORMAL BLOWER
OPERATION
for loose hoses, restriction or
LOW
EVAPORATOR PRESSURE
If ice is blocking evaporator, adjust
suction throttling valve. If cooling
rem ains low, follow diagnosis under
"Normal Evaporator Pressure." If
valve does not respond to adjust­
ment, hoses to and from valve and
suction hose may be restricted or
valve may be defective.
suction throttling
NORMAL
EVAPORATOR PRESSURE
If cooling rem ains low after
pressu re is normal, check
the discharge
EVAPORATOR PRESSURE
REMAINS THE SAME
Valve is stuck open and too much refrig­
erant is entering evaporator. Replace
expansion valve. See Note "E."
Check blower operation.
AIR TEMPERATURE
VARIES
If 7° F. variation at nozzle exist, .
replace suction throttling valve.
See Note "A."
BLOWER NOT
OPERATING
broken wire, loose ground
If iced, check for low evaporator p ressu re.
Adjust suction throttling valve.
remove using vacuum cleaner hose.
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 g la ss. See Note "C."
RESPONDS TO
ADJUST MENT
Check installation of capillary
bulb. If bui» is secured properly
p ressu re. and p ressu re is high, remove
bulb from pipe. See Note "D."
Check for clutch slippage,
belt
for unusual n oises.
I
1
i
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l
BLOCKED
EVAPORATOR
If dirty,
H L _
FOAMING
HIGH
EVAPORATOR PRESSURE
Adjust to normal
evaporator p ressu re.
If unable to adjust-
NO RESPONSE
TO ADJUSTMENT
Repair or replace su c­
tion throttling valve.
HIGH
EVAPORATOR PRESSURE
EVAPORATOR PRESSURE
INCREASES
slippage and listen