Manual Climate Control

The manual climate control system heats or cools the vehicle interior depending on the function selector switch position and the temperature selected. The function selector position determines heating or cooling and air distribution. The temperature blend control setting determines air temperature.

The manual climate control system components are used to select:
- air inlet source (outside or recirculated).
- blower motor speed.
- discharge air temperature (temperature blend).
- discharge air location (defrost, panel, floor).
- A/C compressor clutch operation.

Control System Inputs

Climate Control Assembly
The climate control assembly has three system controls:
- The A/C heater function selector switch combines a vacuum selector valve with two electrical switches to supply battery voltage (B+) to the A/C clutch circuit and the blower motor speed control circuit.
- Temperature selection is accomplished with a potentiometer connected to the electric blend door. Movement of the control knob from COOL (Blue) to WARM (Red) causes a corresponding movement on the air temperature blend door and determines the temperature that the system will maintain.
- The blower motor switch controls blower motor speed by adding or bypassing resistors in the heater blower motor switch resistor.

Evaporator Discharge Air Temperature Sensor
The PCM determines A/C compressor clutch cycling based on input from the evaporator discharge air temperature sensor. The evaporator air discharge temperature sensor:
- maintains evaporator core temperature, and prevents icing of the evaporator core by disengaging the A/C compressor clutch when the evaporator discharge air temperature falls below a preset level, and engaging the A/C compressor clutch when the discharge air temperature rises above a preset level.
- contains a thermistor which receives a reference voltage from the PCM. The thermistor then varies the resistance to the reference voltage based on the evaporator discharge air temperature. The resulting voltage is returned to the PCM where it is interpreted as an evaporator air discharge temperature reading.
- is located in the evaporator core housing just downstream of the evaporator airflow.

Control System Outputs

Blower Motor Switch Resistor
The heater blower motor switch resistor has the following features:
- The assembly is located in the engine compartment on the evaporator housing toward the center of the vehicle.
- Three resistor elements are mounted on the resistor board to provide four blower motor speeds.
- Depending on the heater blower motor switch position, series resistance is added or bypassed in the A/C blower motor circuit to decrease or increase A/C blower motor speed.
- A device to prevent overheating (thermal limiter) will open the resistor coil when the temperature reaches 121°C (250°F) interrupting the blower motor operation in all speeds except HI.
- The thermal limiter cannot be reset and is not serviceable.

A/C Electronic Blend Door Actuator
The A/C electronic blend door actuator is located on the top of the plenum housing.
- Its function is to move the air temperature blend door on command from the temperature control switch.
- The A/C electronic blend door actuator contains a reversible electric motor and a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the air temperature blend door.

Vacuum Control Motors
Vacuum control motors are used to move the floor/panel and panel/defrost doors.