Chevrolet 1977 light duty truck, Руководство по обслуживанию

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DIAGNOSSS
REFRIGERANT SYSTEM
The following is a description o f the type o f
sym ptom each r e frig e ran t co m p o n en t will evidence if a
defect occurs:
C O M P R E S SO R
A com pressor defect will a p p e a r in one o f four
ways: Noise, seizure, leakage, o r low discharge pressure.
N O T E : R eso n an t com pressor noises are not cause
for alarm ; however, irre g u la r noise or rattles m ay
indicate broken parts or excessive clearances due to
wear. To check seizure, de-energize the m agnetic
clutch and check to see if drive plate can be
rotated. If rotation is impossible, compressor is
seized (See "F alse C om pressor Seizure"). To check
for a leak, refer to leak testing in the service
m anual. Low discharge pressure m ay be due to a
faulty internal seal o f the compressor, or a
restriction in the compressor.
Low discharge pressure m ay also be due to an
insufficient re frig eran t charge or a restriction
elsewhere in the system. These possibilities should
be checked prior to servicing the compressor. If the
com pressor is inoperative, but is not seized, check
to see if current is being supplied to the m agnetic
clutch coil terminals.
CO N D E N S E R
A condenser may be defective in two ways: it m ay
leak, o r it m ay be restricted. A condenser restriction will
result in excessive compressor discharge pressure. If a
p artial restriction is present, sometimes ice or frost will
fo rm im m ediately after the restriction as the refrig eran t
expands after passing thro u g h the restriction. If air flow
th ro u g h the condenser or ra d ia to r is blocked, high
discharge pressures will result. D u rin g n o rm al condenser
o peration, the outlet pipe will be slightly cooler than the
inlet pipe.
REC EIVER -D EH YD R A TO R
A defective receiver-dehydrator m ay be due to a
restriction inside the body o f the unit. A restriction at
the inlet to the receiver-dehydrator will cause high h ead
pressures. Outlet tube restrictions will be indicated by
low h e a d pressures and little or no cooling. An
excessively cold receiver-dehydrator outlet may be
indicative o f a restriction.
E X P A N S IO N VALVE
A m a lfu n c tio n o f the expansion valve will be caused
by one o f the following conditions: valve stuck open,
valve stuck closed, broken power element, a restricted
screen o r an im properly located or installed power
elem ent bult. The first three conditions require valve
replacement. The last two may be corrected by replacing
the valve inlet screen and by properly installing the
power ele m ent bulb.
Attachm ent o f the expansion valve bulb to the
evap o rato r outlet line is very critical. The bulb must be
attached tightly to the line and must make good contact
with the line along the entire length o f the bulb. A loose
bulb will result in high low side pressures and poor
cooling.
Indications o f expansion valve trouble are provided
by P erform ance Tests; consult Diagnostic Charts.
VALVE ST U C K O PE N
NO ISY C O M PR ESSO R .
N o Cooling - Freeze Up.
VALVE STU C K CLOSED, BR O K EN PO W ER
E L E M E N T O R P L U G G E D S C R E E N
Very Low Suction Pressure.
N o Cooling.
PO O R L Y LO C A T E D PO W E R E L E M E N T BULB
N o rm al Pressure.
Poor Cooling.
Diagnosis for Defective Valve
The following procedure must be followed to
determ ine if a m alfunction is due to a defective
expansion valve.
1. Check to determ ine if the system will meet the
p erfo rm an ce test as outlined previously. If the expansion
valve is defective, the low pressure readings (evaporator
pressure) will be above specifications.
2. T he loss o f system p erform ance is not as evident
w hen the compressor head pressure is below 200 psi.
Therefore, it m ay be necessary to increase the system
head pressure by partially blocking the condenser.
Disconnect the blower lead wire and rep eat the
"p e rfo rm a n c e check" to determ ine if the evaporator
pressure can be obtained.
3. The system will also indicate a low refrigerant
charge by bubbles occurring in the sight glass.
EVA PO R A TO R
W hen the e v ap o rato r is defective, the trouble will
show up as an in ad eq u ate supply o f cool air. A partially
plugged core due to dirt, a cracked case, or a leaking seal
will generally be the cause.
R EFR IG E R A N T LIN E R E S T R IC T IO N S
Restrictions in the re frig e ran t lines will be indicated
as follows:
1. Suction Line - A restricted suction line will
cause low suction pressure at the compressor, low
discharge pressure and iittle or no cooling.
2. Discharge Line - A restriction in the discharge
line generally will cause the pressure relief valve to open.
3. Liquid Line - A liquid line restriction will be