How the Circuit Works

How the Manual A/C DX, LX, L4: EX Circuit Works

The heater control panel controls the blower controls, air delivery, and A/C compressor controls. With the ignition switch in ON (II), battery voltage is supplied through fuse 30. The heater control panel is grounded at G503.

Blower Controls

The fan speed can be manually selected by turning the fan control dial clockwise, from the OFF position. Turning the dial further clockwise increases the fan's speed, which increases the airflow.

Battery voltage is applied at all times through fuse 21 to the blower motor relay contacts. With the ignition switch ON (II), the blower motor relay is energized which feeds battery voltage to the blower motor. The blower power transistor controls the blower motor in all speeds except HIGH. The blower power transistor is controlled by the heater control panel. When the heater control panel requests HIGH blower speed, the blower power transistor grounds the blower motor, which connects the blower motor directly to ground, making the blower run at high speed.

Air Delivery

The heater control panel controls the blower motor and supplies a 5 VDC reference voltage to the air mix control motor.

The air mix and mode control motors each receive inputs from the heater control panel. The air mix control 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 control dial to select the vents the air flows from, although some air will flow from the dashboard corner vents in all modes. Both the air mix control motor and mode corner vents in all modes. Both the air mix control motor and mode control motor are grounded by the heater control panel.

The recirculation control motor receives battery voltage through fuse 30 with the ignition switch in ON (II). The recirculation control motor regulates the position of the fresh/recirc door, and is controlled by two position inputs from the heater control panel ("Recirc" and "Fresh").

A/C Compressor Controls

Battery voltage is provided at all times to the A/C compressor clutch relay contacts through fuse 12. With the ignition switch in ON (II), battery voltage is supplied to the relay coil through fuse 30.

With the ignition switch in ON (II), the heater control panel grounds the A/C ON input of the ECM/PCM through the multiplex integrated control system and the A/C pressure switch. The ECM/PCM then grounds the A/C compressor clutch relay coil. This energizes the coil, which closes the relay contacts and provides battery voltage through fuse 12 to the A/C compressor clutch. The clutch then engages and begins turning the compressor.

The A/C button at the heater control panel must be pressed to activate the A/C system.

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. When the circuit is open, the relay control module sends a signal through the multiplex integrated control system to the ECM/PCM. Upon receiving the open circuit signal, the ECM/PCM turns off the A/C compressor clutch.

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. The heater control panel, in turn, sends a signal through the A/C pressure switch to the relay control module. The relay control module then sends a signal through the multiplex integrated control system to the ECM/PCM, which turns off the A/C compressor clutch. This prevents condensation from freezing on the evaporator fins and blocking air delivery into the passenger compartment.

How the Climate Control EX-L Circuit Works

The climate control unit controls the blower controls, air delivery, and A/C compressor controls either automatically or semi-automatically. With the ignition switch in ON (II), battery voltage is supplied through 30. The climate control unit is grounded at G503.

Fully-automatic Operation

To put the 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. FULL AUTO will appear 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 the direction of air delivery.

When the temperature is set to its lower limit (60 °F/118 °C) or its upper limit (90 °F/132 °C), the system runs at full cooling or full 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

Various functions of the climate control system can be manually selected in FULL AUTO. All other features remain automatically controlled. Manual selections cause 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 Full Auto mode. The fan speed can be manually selected 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 airflow.

Battery voltage is applied at all times through 21 to the blower motor relay contacts. With the ignition switch ON (II), the blower motor relay is energized which feeds battery voltage to the blower motor. The blower power transistor controls the blower motor in all speeds except HIGH. The blower power transistor is controlled by the climate control unit. When the climate control unit requests HIGH blower speed, the blower power transistor grounds the blower motor, which connects the 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 produce warm air.

Air Delivery

The climate control unit controls the blower motor and supplies a 5 VDC reference voltage to the driver's air mix control motor and the front passenger's air mix control motor.

The air mix and mode control motors all receive inputs from the climate control unit. The driver's and front passenger's air mix motors regulate the mixture of cold and hot air by varying the position of the heater-evaporator doors. The mode control motor controls the direction and volume of outlet air. Use the MODE button to select the vents the air flows from, although 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. The air mix control motors and the mode control motor are grounded by the climate control unit.

The recirculation control motor receives battery voltage through 30 with the ignition switch in ON (II). The recirculation control motor regulates the position of the fresh/recirc door, and is controlled by two position inputs from the climate control unit ("Recirc" and "Fresh").

A/C Compressor Controls

Battery voltage is provided at all times to the A/C compressor clutch relay contacts through 12. With the ignition switch in ON (II), battery voltage is supplied to the relay coil through 30.

With the ignition switch in ON (II), the climate control unit grounds the A/C ON input of the ECM/PCM through the multiplex integrated control system and the A/C pressure switch. The ECM/PCM then grounds the A/C compressor clutch relay coil. This energizes the coil, which closes the relay contacts and provides battery voltage through 12 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.

How the Climate Control EX-L Circuit Works

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. When the circuit is open, the relay control module sends a signal through the multiplex integrated control system to the ECM/PCM. Upon receiving the open circuit signal, the ECM/PCM turns off the A/C compressor clutch.

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. The climate control unit, in turn, sends a signal through the A/C pressure switch to the relay control module. The relay control module then sends a signal through the multiplex integrated control system to the ECM/PCM, which turns off the A/C compressor clutch. This prevents condensation from freezing on the evaporator fins and blocking air delivery into the passenger compartment.