Manual Climate Control

CONTROL COMPONENTS - 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 switch 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
The climate control assembly has four system controls:

Function Selector Switch
The function selector switch is separately serviceable from the integrated control panel (ICP), and 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 Control Switch
The temperature control switch is separately serviceable from the integrated control panel (ICP). Temperature selection is accomplished with a potentiometer connected to the electric blend door. Movement of the temperature control switch from COOL (blue) to WARM (Red) causes a corresponding movement of the temperature blend door.

Blower Motor Switch
The blower motor switch is separately serviceable from the integrated control panel (ICP), and controls blower motor speed by adding or by passing 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 air discharge 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 when the evaporator discharge air temperature falls below a preset level, and engaging the A/C compressor when evaporator 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, and returns the resulting voltage to the PCM. The PCM determines evaporator air discharge temperature based on the return voltage value.
- is located in the heater core and evaporator core housing just downstream of the evaporator airflow.

Control System Outputs

Heater Blower Motor Resistor
The heater blower motor resistor has the following features:
- The assembly is located in the passenger compartment on the heater core and evaporator core housing next to the blower motor assembly.
- 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.
- An overheating device (thermal limiter) will open the resistor coil when the temperature reaches 121°C (250°F) interrupting the blower motor operation in all speeds except high.
- The thermal limiter cannot be reset and is not serviceable.

Temperature Blend Door Actuator
The temperature blend door actuator is located on the rear of the A/C evaporator housing.
- Its function is to move the air temperature blend doors on command from the temperature control switch.

Vacuum Control Motors
The vacuum control motors:
- are located on the A/C evaporator housing, A/C recirculating air duct and heater air plenum chamber.
- direct system airflow to the vehicle interior as determined by the function selector switch.