S-SERIES AIR CONDITIONING -- HEATER SYSTEM
When the VENT knob is turned counterclockwise, air
enters the cab from the hoodscoop and flows through the
instrument panel outlets and floor dump. Except for the
ventilation mode, the knob should be rotated to its full
clockwise position (vent door closed) for all other modes
To Increase the quantity of air entering the cab in the
ventilation mode, the fan may be used to power ventilate.
The fan speed and air outlets can be adjusted for the
desired air flow.
For proper cold weather operation, the heat should be
directed toward the floor. Therefore, close all instrument
panel outlets and fully open the floor dump outlet.
Heating is controlled with the HTR (heat) lever. The full
right HOT position provides the maximum heat. Move
the AIR OUTLETS control lever either to the full cab
position or to any of the other three detented positions in
order to obtain the desired air flow distribution between
cab heat and defrost requirements. For the maximum
air flow, set the fan switch on the H I position. The
heater will also operate with the fan motor in the OFF
position. Air flow is provided by ram air when the truck is
To obtain maximum defrosting, move the HTR lever to
the HOT position and place the AIR OUTLETS lever on
DEF. Adjust the fan speed to provide the desired air
To clear the system of humid air, operate blowers for 30
seconds at HI speed before moving the AIR OUTLETS
lever to the DEF position. This will minimize rapid
fogging of glass, which can occur if humid air is blown
onto a cold windshield.
To improve defroster efficiency, remove ice and/or snow
from glass area.
Control Cable Adjustment
The heater cables on the Heater Only system are self-
adjusting (Figure 18). After the cables have been
installed, move the control levers through two complete
cycles as follows:
Move Defrost lever from Defrost mode to Cab mode and
back to Defrost mode.
Move Heat lever from Heat Off mode to Heat On mode
and back to Heat Off mode.
Repeat each step twice, checking for complete sealing of
the doors in each position.