Chevrolet Light Duty Truck 1973, Service Manual

Page: 104 / 979

1A -78 HEATER A N D AIR C O N D IT I O N I N G
AIR SENSING CAPILLARY
SWITCH
BUMPER
BLOWER SWITCH
Fig. 98- Thermostatic and Blower Switches
3. Remove evaporator core retaining screws and
remove core.
4. Remove blower motor and harness assembly from
case.
Installation
1. Reverse applicable steps in the removal procedure.
CAUTIO N:
Use new "O" rings coated with
clean refrigeration oil when connecting lines.
Add 3 oz. of new refrigeration oil to a new
core.
2. Reverse steps 1-8 of the "Blower Evaporator
Assembly" removal procedure.
3. Evacuate, charge and check the system.
THERMOSTATIC AND/OR BLOWER
SWITCHES
Replacement
1. Remove the cover plate assembly from the
evaporator case.
2. Remove two screws securing either switch to the
cover plate and remove appropriate switch (fig. 98).
3. Install replacement switch, reinstall cover plate and
reverse steps 1-8 of the "Blower-Evaporator
Assembly" removal procedure.
NOTE: When installing thermostatic switch,
be sure to position sensing capillary as when
unit was removed.
RESISTOR
The blower motor resistor is located on the top of the
unit. The entire unit must be removed to replace the
resistor.
FUSE
This Unit does not incorporate an in-line fuse. The lead
wire is connected to the Heater Wiring Harness and
operates off the 20 amp Heater Fuse.
D IA G N O S IS
REFRIGERANT SYSTEM
The following is a description of the type of symptom
each refrigerant component will evidence if a defect
occurs:
Compressor
A compressor defect will appear in one of four ways:
Noise, seizure, leakage, or low discharge pressure (fig.
99).
NOTE: Resonant compressor noises are not
cause for alarm; however, irregular noise or
rattles may indicate broken parts or excessive
clearances due to wear. To check seizure, de­
energize the magnetic clutch and check to see
if drive plate can be rotated. If rotation is
impossible, compressor is seized (See "False
Compressor Seizure"). To check for a leak,
refer to leak testing in the service manual.
Low discharge pressure may be due to a
faulty internal seal of the compressor, or a
restriction in the compressor.
Low discharge pressure may also be due to
an insufficient refrigerant charge or a
restriction elsewhere in the system. These
possibilities should be checked prior to
servicing the compressor. If the compressor is
inoperative, but is not seized, check to see if
current is being supplied to the magnetic
clutch coil terminals.
Condenser
A condenser may be defective in two ways: it may leak,
or it may be restricted. A condenser restriction will result
in excessive compressor discharge pressure. If a partial
restriction is present, sometimes ice or frost will form
immediately after the restriction as the refrigerant
expands after passing through the restriction. If air flow
through the condenser or radiator is blocked, high
discharge pressures will result. During normal condenser
operation, the outlet pipe will be slightly cooler than the
inlet pipe.
Receiver-Dehydrator
A defective receiver-dehydrator may be due to a
restriction inside the body of the unit. A restriction at
the inlet to the receiver-dehydrator will cause high head
LIGHT DUTY TRUCK SERVICE MANUAL