Heating and Air Conditioning: Description and Operation

DESCRIPTION
If the vehicle is equipped with a rear A/C-Heater, this system has two sets of controls. The front set controls the front and rear A/C and heater system. The rear set controls only the rear A/C-Heater

OPERATION
Front Blower Control (Front)
The Front Climate Control Panel receives battery voltage at all times via Fuse 13 (Electron Bat) and ignition voltage from Fuse 21 (Meter). When the Air Flow Control is moved out of the "OFF" position, with the Ignition Switch in "RUN", the Front Climate Control Panel grounds the Front [1][2]Blower Motor Relay. The Front Blower Control Relay energizes, applying battery voltage from Fuses 1 and 2 (Front Blower Motor) to the Front Blower Motor. When the Front Blower Motor Switch is in the "LOW" position, the Front Blower Motor is grounded through each resistor in the Front Blower Motor Resistor Assembly. The Front Blower Motor then runs at low speed. When the Front Blower Motor Switch is moved to the "MED LO" position, the Front Blower Motor Switch decreases the resistance in the motor's ground path by shunting a resistor element in the resistor assembly to ground. The "MED HI" position works in the same way except that two resistor elements within the resistor assembly are bypassed by the Front Blower Motor Switch. When the Front Blower Motor Switch is in the "HIGH" position, the Front Blower Motor is grounded through the Front Blower Motor Switch, bypassing the entire Front Blower Motor Resistor Assembly. The Front Blower Motor then runs at high speed.

Temperature Control (Front)
The temperature control knob controls the Front Blend Door Actuator. The Temperature Blend Door controls the air flow going through or bypassing the heater core. When a temperature range is selected, the Front Climate Control Panel applies a voltage signal to the Front Blend Door Actuator. The actuator motor moves the temperature blend door toward the position selected. The Front Blend Door Actuator sends a position signal back to the control panel. When the voltage feedback signal from the Front Blend Door Actuator indicates that the temperature blend door is in the selected position, the control panel removes voltage from the Front Blend Door Actuator. The temperature blend door rests in the selected position until the temperature control knob is adjusted.

Air Flow Control (Front)
The air flow through the climate control system is controlled by the Mode Actuator. The Mode Actuator controls the air flow through the Heater Assembly. When an air flow mode is selected using the function control buttons, the Front Climate Control Panel applies voltage signals to the Mode Actuator. The Mode Actuator motor moves the mode doors toward the position selected. The Mode Actuator sends a position signal back to the control panel via a series of position switches within the Mode Actuator. When these position switches indicate that the mode doors are in the selected position, the control panel removes voltage from the Mode Actuator. The mode doors remain in the selected position until a different function control mode is selected. The Front Climate Control Panel has direct control over the Fresh/Recirculation Door Actuator. When the Fresh/Recirculation Actuator Control is pushed to the "ON" (recirculation) position the indicator light is lit and voltage is applied to this actuator. The Fresh/Recirculation door is closed, allowing air to be recirculated within the passenger compartment.

Compressor Control
The position of the A/C switch in the Front Climate Control Panel determines if compressor operation is desired. When the switch is depressed, the indicator light is lit and the Front Climate Control Panel applies a ground signal to the Powertrain Control Module via the A/C High Pressure and Low Pressure Switches. The PCM interprets this as a compressor request and decides if conditions are suitable for A/C Compressor operation based on engine sensor information. If conditions are suitable, the PCM applies a ground signal to the [1][2]A/C Relay #1 Coil. This energizes the relay and it applies voltage to the A/C Compressor Clutch Coil. The A/C compressor turns with the engine, forcing A/C refrigerant to cool the evaporator and supply the passenger compartment with cool air. If the A/C High or Low Pressure Switches open, the compressor request signal to the PCM is interrupted. This causes the PCM to de-energize A/C Relay #1 and causes the compressor clutch to disengage.

Blower Controls (Rear)
The Rear Blower Motor can be controlled from the Rear Blower Motor Switch (rear) or the Rear Blower Motor Switch (front). The Rear Blower Motor receives battery voltage from Fuses 4 and 5 at all times. The Rear Blower Switch (front) enables the Rear Blower Motor Switch (rear) when the Rear Blower Motor Switch (front) is in the "REAR" position, by grounding the wiper of the rear switch. This ground signal is switched via the Front Climate Control Panel. This allows only one control at a time to regulate the rear blower speed. When the Rear Blower Motor Switch (front) is in position "1," the Rear Blower Motor is grounded through each resistor in the Rear Blower Motor Resistor Assembly. The Rear Blower Motor then runs at low speed. When the Rear Blower Motor Switch is moved to position "2," the Rear Blower Motor Switch decreases the resistance in the motor's ground path by shunting a resistor element in the resistor assembly to ground. Position "3" works in the same way, except that two resistor elements within the resistor assembly are bypassed by the Rear Blower Motor Switch (front). When the Rear Blower Motor Switch (front) is in position "4", the Rear Blower Motor is grounded through the Rear Blower Motor Switch (front), bypassing the entire Rear Blower Motor Resistor Assembly. The Rear Blower Motor then runs at high speed. The Rear Blower Motor Switch (rear) operates like the Rear Blower Motor Switch (Front) when the Rear Blower Motor Switch (Front) is in the "REAR" position.

Air Flow Control (Rear)
The air flow through the rear climate control portion of this system is controlled by the rear vent door actuator. The Rear Vent Door Actuator controls the air flow through the heater and A/C assembly. Rear air flow is controlled by the rear vent door via the Rear Climate Control Panel. The rear vent door is moved by the Rear Climate Control Panel applying voltage to the rear vent door actuator. The Rear Vent Door Actuator moves the rear vent door toward the position selected.

Temperature Control (Rear)
The temperature control knob controls the Rear Blend Door Actuator. The rear blend door controls the air flow going through or bypassing the rear heater core. When a temperature range is selected, the Rear Climate Control Panel applies a voltage signal to the Rear Blend Door Actuator. The actuator motor moves this temperature blend door toward the position selected. The Rear Blend Door Actuator sends a position signal back to the Rear Climate Control Panel. When the voltage feedback signal from the Rear Blend Door Actuator indicates that the temperature blend door is in the selected position, the control panel removes voltage from the Rear Blend Door Actuator. The rear blend door rests in the selected position until the temperature control knob is adjusted. When the Rear Blower Motor is "OFF", voltage is applied to the Rear Water Valve Solenoid. The solenoid is energized and engine coolant is blocked from flowing through the rear heater core. When the Rear Blower Motor is not in "OFF", a ground signal from either rear Blower Switch is applied to the rear Climate Control Panel. The Rear Climate Control Panel removes voltage from the Rear Water Valve Solenoid. The solenoid is de-energized and engine coolant is allowed to flow through the rear heater core.