GMC 4000 Series Service Manual page 78

When cab begins to cool, close windows tightly and
move "AIR" lever to "NORMAL" position to pro­
vide desired mixture of both recirculated air and
outside air. As required, "TEMP" lever can be
moved towards "HOT" position to allow mixing of
hot and cool conditioned air as required for com­
fortable system outlet temperatures.
OPERATING HEATING SYSTEM ONLY
For heating only, move "AIR CONDITION"
lever to "OFF" and "AIR" lever to "OUTSIDE."
Position "TEMP" lever as required for desired
Keep cowl vent air intakes closed when operating in congested traffic to prevent
deadly exhaust gases from entering cab.
Exhaust gases may have strong odors which normally should give warning of
their presence. However, the exhaust gases from some vehicles may not be so not­
iceable under certain conditions and the senses of people react differently. Exhaust
gases contain a percentage of carbon monoxide which is poisonous gas that, by it­
self, is tasteless, colorless, and odorless.
G M C S E R V I C E M A N U A L
temperature of incoming air. Should defogging of
windshield be required, open door ventilator win­
dow slightly, place "DEFROST" lever to extreme
right "ON" position, and operate blower motor at
high speed.
tioning, place "AIR CONDITION," "DEFROST,"
and "TEMP" levers in extreme left positions,
move "AIR" lever to extreme right position, then
place fan switch lever to desired speed position.
Air flow will be directed through heater outlets
and not "A/C" outlets.
V EN T ILA T IO N
W ARNING - CARBO N MONOXIDE
AIR CONDITIONING
For warm weather ventilation less air condi­
Sec. 1
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