GMC 1976 ZEO 6083 Maintenance Manual page 123

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AIR CONDITIONING SYSTEM
HEATING SYSTEM (WITHOUT AIR CONDITIONING)
CONTROL OPERATION
The heating system controls (figure 1) are located
on the instrument panel to the right of the steering
column . There are three separate controls :
"FAN" lever to control speed of blower operat-
ion; "RECIRC," "COLD," "HOT" lever to control
temperature of air ; "OFF," "VENT," "HEATER,"
"DEF" lever to control direction of air flow. The
"FAN" lever works vertically and the other two
levers work horizontally . The three levers may be
placed in any combined position to deliver the cli-
mate conditions most desirable at any given time.
"Type 1 Fan" (figure 1) - The fan switch has
four positions; "OFF" and three blower speeds rang-
ing to "HI" and two unmarked positions between
"OFF" and "HI." The fan will not operate unless the
top lever has been moved from the "OFF" position,
and in order to operate the fan in the "HI" position
the engine must be running.
"Type 2 Fan" (figure 2) - The fan switch has
four positions; "LO" and three blower speeds rang-
ing to "HI" . Fan will operate whenever the key is in
the "RUN" or "ACCESSORY" position . In order to
operate the fan in the "HI" position the engine must
be running.
"OFF," "VENT," "HEATER," "DEF" -
With the lever in the "OFF" position the system is
off. With the lever in the "VENT" position 100%
outside air enters the driver's compartment. The air
enters through the dash mounted outlets and
Figure 1-Heating System Controls, Type 1
through the heater outlets. Temperature of incoming
air may be controlled by moving the "RECIRC,"
"COLD," "HOT" (temperature) lever to desired po-
sition . Any one of the three blower speeds may be
selected .
With the lever in the "HEATER" position, air
will flow through the heater floor distributor outlet
(with slight flow of air to the defroster outlet). For
maximum heat, move temperature lever to "HOT"
position and "FAN" switch lever to "HI" position .
Heating system output can be varied by moving tem-
perature lever and "FAN" lever to different posi-
tions.
With the lever in the "DEF" position, the system
operates the same as in the "HEATER" position
except most of the air flow will be through the de-
froster outlets at the windshield .
"RECIRC," "COLD," "HOT" - This lever,
used in conjunction with the system selector lever
("OFF," "VENT," "HEATER," "DEF") and the
"FAN" switch lever, will control the temperature of
the output air being distributed.
Clear windshield, rear window, outside mirror,
and all side windows of ice and snow before driving
vehicle .
Operate blower on "HI" for a few seconds before
moving the vehicle, to clear the air intakes of snow .
Figure 2-Heating System Controls, Type 2