Chevrolet 70 Series 1970, Service Manual

Page: 171 / 841

CAB AND BODY MOUNTINGS 1-140
INSUFFICIENT COOLING DIAGNOSIS CHART
CHECK AIR FLOW
i _ r
NORMAL AIR FLOW
Inspect sy stem fo r visual de-
fe e ts. Check air, tem p e ra tu re.
NO OR LOW AIR FLOW
Check blow er operation.
HIGH AIR
TEMPERATURE
---------
NORMAL AIR
TEMPERATURE
■
AIR TEMPERATURE
VARIES
—
1
Check sight g las s.
Check for a ir leaks at cab doors,
If 7 °F
variatio n at nozzle
windows, cowl, o r unit d rain hose.
Note "A."
-ZL.
BLOWER NOT
OPERATING
Check fo r blown fuse, defective blower
sw itch,
broken w ire, loose ground
----
i
NORMAL BLOWER
w ire, defective blow er m otor.
1
-------
BLOCKED
OPERATION
EVAPORATOR
Check for loose hoses, re s tric tio n or
leakage in a ir ducts, p a rtially clo sed a ir
outlet valve o r clogged ev ap o rato r co re.
If iced, check for low ev ap o rato r p r e s s u r e .
Check P.O.A. function o r adjust*S.T. valve. If
d irty , rem ove using vacuum c lean er hose.
NO FOAMING
-------- i--------
FOAMING
Check ev ap o rato r p re s s u re .
System is probably low on re frig e ra n t. Check for
leaks, re p a ir and add re frig e ra n t. If foaming still
o c cu rs check for re s tric tio n in re frig e ra n t sy stem
between condenser and sight g la s s. See Note "C ."
NORMAL
LOW
HIGH
EVAPORATOR PRESSURE
EVAPORATOR PRESSURE
EVAPORATOR PRESSURE
Check - c o m p re ss o r
d isc h arg e p re s s u re .
COMPRESSOR HIGH
DISCHARGE PRESSURE
Check fo r a ir in sy stem , excess
re frig e ra n t, re s tric tio n in con­
d e n se r r e frig e ra n t tu b es o r a ir
fin s. See Note "B."
If ice is blocking ev ap o rato r, check P.O.A.
valve function o r adjust’s .T . valve. If cooling
re m a in s low, follow diagnosis under "N orm al
E vaporator P r e s s u r e ." If P.O.A. valve is
functioning p ro p e rly , o r 'S .T . valve does not
respond to adjustm ent, hoses to and from
^valve and suction hose may be re s tric te d , o r
S.T. valve may be defective.
Check P.O .A . valve operation
a s above, o r adjust S.T . valve.
COMPRESSOR LOW
DISCHARGE PRESSURE
Check for low re frig e ra n t, re stric tio n
in liquid line, plugged o r defective ex­
pansion valve, o r defective co m p resso r
o r P.O .A . o r *S.T. valve. See "Note C."
P.O .A . VALVE OPERATING
PROPERLY OR*S.T. VALVE
RESPONDING TO
ADJUSTMENT
IF NOT
FUNCTIONING OR
RESPONDING
TO ADJUSTMENT
R eplace P.O.A. o r S.T. valve.
NORMAL
HIGH
EVAPORATOR PRESSURE EVAPORATOR PRESSURE
COMPRESSOR NORMAL
DISCHARGE PRESSURE
If cooling re m a in s low after
p r e s s u r e is norm al, check
the d isch arg e p re s s u re .
Check in stallatio n of cap illary
bulb. If bulb is se c u re d p ro p e rly
and p r e s s u r e is high, rem ove
bulb from pipe. See Note "D ."
Check fo r p ro p e r se a l around
ev ap o ra to r c o re and te m p e r­
a tu re door.
*S.T. - Suctioning Throttling.
EVAPORATOR PRESSURE
REMAINS THE SAME
EVAPORATOR PRESSURE
INCREASES
Valve is stuck open and too much r e fr ig ­
e ran t is en terin g ev ap o rato r. Replace
expansion valve. See Note "E ."
Check fo r clutch slippage,
belt slippage and listen
fo r unusual n o ise s.
t
-6878
Figure 35—Diagnosis Chart for Air Conditioning
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL