Chevrolet 1977 light duty truck Service Manual page 60

Fig. IB -13-O verhead U n it Control (C-K Models)
lever on COLD, blower switch on HI and the
overhead unit blower switch should be on HI.
C 6 0 SYSTEM (G M O DELS)~FIG . IB -1 4
The system selector
determ ines the mode o f operation: OFF, MAX, N O R M ,
HEAT, D E F O G or D EF. W hen the system selector lever
is placed in the A /C ,
connection is m ade to the compressor clutch through the
control panel switch and the discharge pressure switch. If
the switch is closed (am bient tem perature above 4 .4 XI.),
the compressor will run. In the O FF, HEAT, D E F O G or
D E F positions, the compressor is not energized.
The system selector
direction o f outlet air flow. M oving the lever from mode
to mode varies the position o f a rotary vacuum valve on
the control. The position o f the vacuum valve will supply
vacuum to, or vent, vacuum diaph rag m s which position
the air and defroster doors in the heater distributor duct
and the outside air door in the right side o f the cowl
plenum. The position o f these doors determines if ouput
air flow is from the A / C outlets using recirc air (MAX),
or recirc and outside air (N O R M ), the heater outlet
(HEAT), heater and defroster outlets (D E FO G ), or the
defroster nozzles with slight air flow from the heater
outlet (DEF).
Tem perature Control
(A /C Modes)
T he tem perature lever activates a potentiom eter on
the control assembly (connected
Fig. 1B-14--C60 System Controls (G Models)
lever (air control lever)
positions, electrical circuit
lever also determines the
in series with the
amplifier on the control
evaporator) to control compressor operation.
(Heater-Defrost Modes)
The tempeature lever determ ines the tem perature of
outlet air flow by positioning the tem perature door in the
heater distributor assembly, through the motion o f a
bowden cable linking the control panel lever to the
tem perature door.
Fan Switch
The blower (FAN ) switch provides a means of
selecting the am ount o f air flow from the system by
regulating the speed of the heater or A /C blower motor.
There is no O F F position on the fa n switch; however the
blower is inoperative if the selector lever is placed in the
O F F position. If the selector lever is placed in any of the
heater or A /C modes,
operative. The blower speeds available are LO, M l, M2
and HI.
O VERHEAD SYSTEM (G MODELS)
This system opeates in conjunction with the C60
system. Since refrigerant is controlled by the C60 system,
the only control provided on the rear overhead system is
a three speed blower switch (fig. 1B -15).
In the O F F position, the blower is inopertive;
however, refrigerant is circulating in the system if the
front system is ON. To operate the rear overhead system,
simply select the desired blower speed (LOW, MED, HI).
W hen air circulation only is desired, the rear A /C
Fig. IB-15-O verhead U nit Control (G Models)
Fig. lB -1 6 -M o to r Home U n it Control
and th e rm iste r on the
the appropriate blower is