Control Assembly: Description and Operation

The control components consist of:





Item Description
1 Heater Blower Motor Switch
2 Temperature Control Switch
3 Function Selector Switch
4 Heated Back Window Switch
5 Heater Temperature Cable
6 Panel Airflow Door Vacuum Control Motor
7 Defrost/Floor Door Vacuum Control Motor
8 A/C Blower Motor Resistor
9 Air Inlet Door Vacuum Control Motor

The manual climate control system heats or cools the vehicle depending on the function selector position and the temperature selected. Function selector position determines heating or cooling and air distribution. The temperature control setting determines air temperature. The heated back window switch operate the heated back window.

CONTROL SYSTEM INPUTS
The climate control system inputs are used to:
^ Select air inlet source (fresh/recirculated). Select blower motor speed.
^ Select discharge air temperature (temperature blend).
^ Select discharge air location (defrost, panel, floor).
^ Select A/C compressor clutch operation. Select heated back window operation.





CONTROL SYSTEM OUTPUTS
Air Management Doors
The air management doors are operated by vacuum control motors and a heater temperature cable. The A/C air inlet door and distribution doors are controlled by vacuum control motors and the function selector switch. The air temperature control door is controlled by the heater temperature cable and the temperature control switch.

Blower Motor Circuit
The blower motor circuit consists of the heater blower motor switch, the A/C blower motor resistor and the A/C blower motor. Blower motor speed is determined by changing the current flow to the A/C blower motor using resistors. The heater blower motor switch has four speeds that are obtained using three resistors that are wired in series. The A/C blower motor resistor is wired into the A/C blower motor ground circuit.
^ High Speed - Current through the A/C blower motor bypasses all resistors and travels directly to ground.
^ Medium High Speed - Current travels through one resistor and then to ground, slowing down current flow and the A/C blower motor.
^ Medium Low Speed - travels through two resistors and then to ground, slowing down current flow and the A/C blower motor.
^ Low Speed - Current travels through all three resistors, adding the highest resistance and causing the A/C blower motor to run at its slowest speed.
The thermal limiter is integral to the A/C blower motor resistor and serves as a temperature protection device. The thermal limiter is wired in series with the A/C blower motor resistor and opens when the resistor reaches approximately 121° C (250° F). When the thermal limiter opens, the A/C blower motor will only operate at high speed. The thermal limiter does not reset; once open, the A/C blower motor resistor must be replaced.

Compressor Clutch Circuit
An A/C clutch drives the A/C compressor shaft. When voltage is applied to the A/C clutch field coil, the clutch plate and hub assembly (which is connected to the A/C compressor shaft) is drawn by magnetic force toward the A/C clutch pulley, which rotates freely on the A/C compressor front head casting. The magnetic force locks the clutch plate and hub assembly and the A/C clutch pulley together as one unit. The A/C compressor shaft then turns with the A/C clutch pulley. When voltage is removed from the A/C clutch field coil, springs in the A/C clutch move the clutch plate away from the A/C clutch pulley and the A/C compressor shaft stops rotating.

Heated Back Window
The heated back window switch supplies power to the heated back window grid wires. The heated back window switch operates through the safety belt warning chime to limit the time of operation to fifteen minutes. If more time is necessary to clear the back window, the heated back window switch can be pressed again for another fifteen minutes of operation. The heated back window switch is mounted in the Integrated Control Panel (ICP) and cannot be repaired separately.