How the Circuit Works

How The Front Blower Controls Circuit Works

Voltage is applied at all times through fuse 56 to the blower motor relay contacts. With the ignition switch ON (II), the front blower motor relay is energized which feeds battery voltage to the blower motor.

The heater fan switch then applies ground to the front blower resistor for the desired blower motor speed. Each time you turn the heater fan switch to a higher speed, more segments of the front blower resistor are bypassed. This increases the blower speed. When the heater fan switch is in position 4, the entire resistor is bypassed and the blower motor runs at the highest speed.

How The Rear Blower Controls Circuit Works

Either the rear heater-A/C main switch (front control) or the rear heater-A/C passenger control panel (rear control) controls the rear-A/C blower motor. Voltage is provided at all times to the rear- A/C blower motor through fuse 60. With the ignition switch ON (II), voltage is provided to the coils of the rear blower motor low, middle, high, and main relays through fuse 3 (in the driver's under-dash fuse/relay box).

Front Control
When you turn the rear heater-A/C main switch to the low, middle, or high position in either the cool or hot mode, the corresponding rear blower motor relay is grounded. Grounding the relay energizes its coil and provides ground to the rear blower resistor. Each time you turn the main switch to a higher speed, more segments of the rear-A/C blower resistor are bypassed. This increases the rear-A/C blower motor speed. Additionally, when the main switch is in the high position and in the cool mode, the rear blower motor main relay is also grounded. Grounding the relay energizes its coil and the entire resistor is bypassed. The rear-A/C blower motor runs at the highest speed.

Rear Control
When you turn the rear heater-A/C main switch to the rear position, ground is supplied to the rear heater-A/C passenger control panel. When you turn the rear heater-A/C passenger control panel to the low, middle, or high position in either the cool or hot mode, the corresponding rear blower motor relay is grounded. Grounding the relay energizes its coil and provides ground to the rear blower resistor. Each time you turn the control panel to a higher speed, more segments of the rear blower motor resistor are bypassed. This increases the rear-A/C blower motor speed. Additionally, when the control panel is in the high position and in the cool mode, the rear blower motor main relay is also grounded. Grounding the relay energizes its coil and the entire resistor is bypassed. The blower motor runs at the highest speed.

How The Front Air Delivery Circuit Works

The heater control panel receives battery voltage at all times through fuse 13. With the ignition switch ON (II), voltage is supplied to the control panel through fuse 3. The control panel is grounded at G401. It controls the blower motor, and supplies a 5 VDC reference voltage to the air mix control motor.

The air mix and front mode control motors each receive inputs from the control panel. The air mix motor regulates the mixture of cold and hot air by varying the position of the heater-evaporator door. The front mode control motor controls the direction and volume of outlet air. The air flow can be directed to the dashboard vents or the corner vents. Both the air mix control motor and front mode control motor are grounded by the control panel.

The recirculation control motor receives battery voltage through fuse 3 when the ignition switch is ON (II). It regulates the position of the fresh/recirc door, and is controlled by two position inputs from the control panel ("Recirc" and "Fresh").

How The Rear Air Delivery Circuit Works

Either the rear heater-A/C main switch (front control) or rear heater-A/C passenger control panel (rear control) controls the rear air delivery. With the ignition switch ON (II), voltage is provided to the to the rear mode control motor and the rear mode control motor relay coil through fuse 3.

From the Front (Dashboard Dial)
When you turn the rear heater-A/C main switch counterclockwise (cool mode) from the OFF position, ground is provided through the rear heater-A/C passenger control panel to the BLU/YEL wire of the rear mode control motor. The motor moves the rear mode door so that the air flows from the rear ceiling vents.

When you turn the rear heater-A/C main switch clockwise (hot mode) from the OFF position, ground is provided to the rear mode control motor relay. When the dial is in the middle or high position, ground is provided through the normally closed contacts of the relay to the GRN/RED wire of the rear mode control motor. When the dial is in the low position, ground is also provided to the coil of the relay. Grounding the relay energizes its coil providing ground to the GRN/WHT wire of the motor through the closed contacts of the relay. Regardless of which wire is grounded, the motor moves the rear mode door to a position that directs air flow out the rear floor vents.

From the Rear (Passenger's Control Panel)
When you turn the rear heater-A/C main switch to the rear position (RR), ground is supplied to the rear heater-A/C passenger control panel.

When you turn the air flow control dial (in the rear heater-A/C passenger control panel) to the cool mode, ground is provided to the BLU/YEL wire of the rear mode control motor. The motor moves the rear mode door so that air flows from the rear ceiling vents.

When you turn the air flow control dial (in the rear heater-A/C passenger control panel) to the hot mode, ground is provided to the rear mode control motor relay. When the dial is in the middle or high position, ground is provided through the normally closed contacts of the relay to the GRN/RED wire of the rear mode control motor. When the dial is in the low position, ground is also provided to the coil of the relay. Grounding the relay energizes its coil providing ground to the GRN/WHT wire of the motor through the closed contacts of the relay. Regardless of which wire is grounded, the motor moves the rear mode door to a position that directs air flow out the rear floor vents.

How The A/C Compressor Controls Circuit Works

Voltage is provided at all times to the heater control panel through fuse 13, and to the A/C compressor clutch relay contacts through fuse 59. With the ignition switch ON (II), voltage is supplied to the control unit and the relay coil through fuse 3. The control panel is grounded at G401.

When you push the A/C button ON with the ignition switch ON (II) and the heater fan switch not in the OFF position, the control panel will ground the A/C ON input of the PCM through the A/C pressure switch. The PCM then grounds the coil in the A/C compressor clutch relay. This energizes the coil, which closes the relay contacts and provides voltage through fuse 59 to the compressor clutch. The clutch then engages and begins turning the compressor.

Evaporator Temperature Sensor
The evaporator temperature sensor is located on the evaporator housing. If the temperature at the evaporator gets too cold, the evaporator temperature sensor sends a signal to the heater control panel to turn off the A/C compressor clutch. This prevents condensation from freezing on the evaporator fins and blocking air delivery into the passenger compartment.

A/C Pressure Switch
The A/C pressure switch is located in the condenser outlet line where refrigerant is in a high temperature, high pressure liquid state. The switch will sense abnormally high or low pressure, and open the circuit. This removes the ground signal from the PCM, and turns off the compressor.

How The Front Air Delivery Circuit Works

The climate control unit controls the blower controls, air delivery, and A/C compressor controls either automatically or semi-automatically. The control unit receives battery voltage at all times through fuse 13. With the ignition switch in ON (II), battery voltage is supplied through fuse 3. The control unit is grounded at G401.

Fully-automatic Operation
To put the automatic climate control in fully automatic mode, press the AUTO button and set the fan control dial to AUTO, then set the desired temperature by turning the temperature control dial. You will see FULL AUTO in the system's display.

The system automatically selects the proper mix of cooled and/or heated air that will, as quickly as possible, raise or lower the interior temperature from its current level to the set temperature. The system also adjusts the fan speed and changes direction of air delivery.

When you set the temperature to its lower limit (60 °F/18 °C) or its upper limit (90 °F/32 °C), the system runs at full cooling or heating only. It does not regulate the interior temperature. When the temperature is set between the lower and upper limits, the system regulates the interior temperature to the set value.

Semi-automatic Operation
You can manually select various functions of the climate control system when it is in FULL AUTO. All other features remain automatically controlled. Making a manual selection causes the word FULL to go off.

However, when you select A/C OFF, the system cannot regulate the inside temperature if you set the dial lower than the temperature outside.

Blower Controls
The fan speed is automatically controlled in the fully-automatic mode. You can manually select the fan speed by turning the fan control dial clockwise, just past the AUTO position. This takes the fan from automatic mode to its lowest manually controlled speed. Turning the dial further clockwise increases the fan's speed, which increases air flow.

Battery voltage is applied through fuse 56 to the front blower motor relay contacts at all times. With the ignition switch ON (II), the front blower motor relay in the under-hood fuse/relay box is energized which feeds battery voltage to the front blower motor. The blower power transistor controls the front blower motor in all speeds except HIGH. The blower power transistor is controlled by the climate control unit. When the control unit requests HIGH blower speed, it grounds the front blower motor HIGH relay coil, energizing the relay, which connects the front blower motor directly to ground, making the blower run at high speed.

In cold weather, the blower will not come on automatically until the heater starts to develop warm air.

Air Delivery
The climate control unit controls the front blower motor and supplies a 5 VDC reference voltage to the air mixture control motor.

The air mix and mode control motors each receive inputs from the control.unit. The air mix motor regulates the mixture of cold and hot air by varying the position of the heater-evaporator door. The mode control motor controls the direction and volume of outlet air. Use the MODE button to select the vents the air flows from. Some air will flow from the dashboard corner vents in all modes. Each time you press the MODE button, the display shows the mode selected. Press the button four times to see all the modes. Both the air mix control motor and mode control motor are grounded by the control unit.

The recirculation control motor receives battery voltage through fuse 3 when the ignition switch is ON (II). It regulates the position of the fresh/recirc door, and is controlled by two position inputs from the control unit ("Recirc" and "Fresh").

A/C Compressor Controls
Voltage is provided at all times to the A/C compressor clutch relay contacts through fuse 59. With the ignition switch ON (II), voltage is supplied to the relay coil through fuse 3.

With the ignition switch ON (II), the climate control unit grounds the A/C ON input of the PCM through the A/C pressure switch. The PCM then grounds

the A/C compressor clutch relay coil. This energizes the coil, which closes the relay contacts and provides voltage through fuse 59 to the A/C compressor clutch. The clutch then engages and begins turning the compressor. By default, when the climate control system is on, the A/C is on.

Evaporator Temperature Sensor
The evaporator temperature sensor is located on the evaporator housing. If the temperature at the evaporator gets too cold, the evaporator temperature sensor sends a signal to the climate control unit to turn off the A/C compressor clutch. This prevents condensation from freezing on the evaporator fins and blocking air delivery into the passenger compartment.

A/C Pressure Switch
The A/C pressure switch is located in the condenser outlet line where refrigerant is in a high temperature/high pressure liquid state. The switch will sense abnormally high or low pressure, and open the circuit. This removes ground from the PCM, and turns off the compressor.