K 2500 Truck 4WD V8-379 6.2L DSL VIN C FI (1989)
Air Door Actuator / Motor: Description and Operation
The Valves which control the flow of air through the Heater and A/C Module are positioned by electric Motors. There is one Motor and one Position
Potentiometer for each Valve. The Position Potentiometer indicates the position of the Valve at any time to the Heater and A/C Controller by means of
a voltage level.
There are two drive circuits for each Motor in the Controller which can operate the Motors in either direction. When the Motors are not running, both
outputs are held at ground by the two drivers. When any Motor is to operate, one of the drivers supplies approximately 7.5 volts to one side of the
Motor depending on the direction it is to run.
The Air Inlet Valve is normally in the position which allows outside air to enter the system. In this position, the Air Inlet Valve Potentiometer returns
about 4.9 volts to the Heater and A/C Controller. When the A/C Button is depressed, and if the temperature setting is at full Cold and the blower is set
to MED or HI, the Air Inlet Valve Motor will move the valve to the recirculating position 30 seconds after the Air Inlet Pressure Switch closes.
The Air Inlet Valve is opened again, 5 minutes after the Air Inlet Pressure Switch opens. It opens immediately if the temperature setting is raised, the
blower speed is reduced to Low, or the air flow is directed to the floor outlets.
The Temperature Valve Motor positions the temperature Valve according to the Temperature setting of the Heater and A/C Controller. For the full
Cold temperature setting, the Valve is in the cold position and the Temperature Valve Potentiometer returns about 0.5 volts to the Heater and A/C
Controller As the temperature setting is changed to full HOT the Temperature Valve is moved to the warm positions, and the potentiometer output
rises to about 4.9 volts. For a temperature setting in the mid range, the Temperature Valve is positioned to a point where the potentiometer output is
the same as the preprogrammed value for the selected setting.
The Mode Valve Motor operates in a manner similar to that for the Air Inlet Valve and Temperature Valve and is positioned according to the Mode
selected. For full A/C, the potentiometer output is about 0.2 volts and for full DEFROST the output is about 4.8 volts. In the Heat Mode, the
potentiometer output is about 2.5 volts.
Should any of the Motors stall when changing a Valve location, voltage is removed by the Heater and A/C Controller after 45 seconds, to protect the
Motor This sequence will be repeated each time there is a change in the Mode setting.
