Some extra info
Fan Speed Control
The A/C and heater system blower motor fan is controlled by a four position rotary switch located on the left side of the climate control head. The operating speeds are: LOW, MEDIUM LOW, MEDIUM HIGH, and HIGH. These operating speeds are controlled by three resistors wired in a series in the A/C blower motor resistor A/C blower motor resistor (19A706). The resistor assembly also has a thermal limiter which acts as a temperature sensitive fuse.
l In the LOW position, current flows through all three resistors.
l In the MEDIUM LOW position, current flows through two of the resistors.
l In the MEDIUM HIGH position, current flows through one resistor.
l In the HIGH position, current flow bypasses the resistors.
The limiter will open at approximately 121ºC (250ºF) and interrupt the circuit for all speeds except HIGH. Once opened, the limiter cannot be reset. The resistor assembly must be replaced.
Airflow Control
The A/C damper door switch , located on the right side of the control head, allows the flow of heated or cooled air to be directed through the duct system by means of vacuum operated motors opening and closing doors within the air plenum chamber. This switch activates the A/C clutch control circuit and allows the operation of the blower motor fan.
l The PANEL, PANEL/FLOOR, FLOOR, DEFROST/FLOOR, and DEFROST positions are shown as icons on the control head. OFF, MAX A/C, and A/C are printed.
l In the OFF position, all climate control functions cease. The outside air inlet door is closed and the blower motor fan circuit is shut off.
l The MAX A/C position opens the recirculating air door, closes off the outside air inlet, and engages the A/C clutch circuit. The air is directed to the instrument panel registers.
l The A/C position closes the recirculating door, opens the outside air inlet allowing outside air to enter and continues the A/C clutch circuit. The air continues to exit through the panel registers.
l The PANEL position allows outside air to flow through the panel registers with the A/C system off.
l With the A/C system on, the PANEL/FLOOR position allows outside air to flow between the panel registers and the floor outlets.
l The FLOOR position directs outside air through the floor outlets.
l With the A/C system on, the FLOOR/DEFROST position directs the outside air to flow between the floor outlets and the windshield defroster nozzles.
l With the A/C system on, the DEFROST position directs outside air to flow through the defroster nozzles only.
Temperature Control
The temperature of the incoming air is controlled by the middle switch in the control head. This switch controls the position of the blend air door inside the air plenum chamber. The incoming air is directed through or around the heater core by the position of the blend air door, raising or lowering the temperature.
Vacuum System
The vacuum system is the source of power for the function of the mode doors. Engine vacuum is supplied to and stored in the vacuum reservoir, which is located on top of the right frame rail behind the headlight assembly. A vacuum check valve is built into the reservoir. The vacuum is routed to the function control switch, the vacuum motors, and the heater core water control valve through a color-coded vacuum hose harness.
