Front Temperature Controls

The Temperature Valve Actuator Motor operates in response to a voltage signal form the Heater and A/C Controller's Temperature Control knob. The Temperature Valve Actuator Motor has operating voltage applied when the Ignition Switch is in RUN from HTR-A/C Fuse 12 through the BRN (141) wire. The motor is grounded through the BLK (150) wire to Ground G201. The motor positions the Air Temperature Valve in a position consistent with the voltage signal from the Heater and A/C Controller. This signal is delivered to the actuator motor on the LT BLU (733) wire.

The Heater and A/C Controller is also powered from HTR-A/C Fuse 12 through the BRN (141) wire. It also is grounded through the BLK (150) wire to Ground G201. In the controller, current flows to ground through a rheostat. The wiper arm of the rheostat is moved by the Temperature

Control knob to select a portion of the voltage dropped across the resistance. This voltage is delivered to the actuator motor to position the valve.

The Heater and A/C Controller's Temperature Control rheostat also contains a vacuum switch detent position. When the knob is fully counter-clockwise in the cold direction, the vacuum switch is in effect a closed vacuum valve. The Water Valve which allows coolant flow through the heater core is closed. When the switch is turned slightly clockwise in the hot direction, the vacuum switch operates as an open valve allowing engine vacuum to open the Water Valve. Heated engine coolant can then flow through the heater core to heat the passing air.

Vacuum is used to operate the Water Valve and the air delivery valves. Vacuum is provided by the operation of the Gasoline Engine or by the operation of the Diesel Engine's Vacuum Pump. A Vacuum Tank is installed to provide vacuum capacity for valve operations. Vacuum is established in the tank after a few minutes of engine/vacuum pump operation. There may be some slight delay in the positioning of the air delivery valves and the Water Valve just after the engine is started. After the engine stops, vacuum is retained in the tank for a period of time but is eventually lost.

Two vacuum supplies are routed to the Heater and A/C Controller. The BLK vacuum tube from the Vacuum Tank is routed through a grommet to the vacuum tube connector located near the heater. One BLK vacuum tube leaves this connector for vacuum supply to the Heater and A/C Controller. A vacuum tube splice in the vacuum tube harness provides two separate vacuum tubes for connection at the Heater and A/C Controller. The BLK vacuum tube for operation of the Water Valve connects to Pin 1 of the side connector at the Mode Switch. The BLK vacuum tube for operation of the air delivery valves connects at Pin 6 on the body of the Mode Switch.