Heating and Air Conditioning: Description and Operation

1. HEATER BLOWER OPERATION
(Manual blower operation)
When the blower control SW is set to any blower speed, the A/C control assembly operates and the current to drive the blower motor flows from TERMINAL BLW of the A/C control assembly to TERMINAL SI of the blower motor control relay. The current activates the relay and the voltage applied to TERMINAL +B of the blower motor control relay is output to TERMINAL M+ of the relay as the voltage for the selected blower speed. The current then flows from TERMINAL M+ of the blower motor control relay to TERMINAL 2 of the blower motor to TERMINAL 1 to TERMINAL M- of the blower motor control relay to TERMINAL GND to GROUND, and the blower motor operates at the blower speed selected.

(Auto function)
When the auto SW is turned ON, the A/C control assembly calculates the required vent temperature based ON the set temperature and input from each sensor. Then TERMINAL BLW of the A/C control assembly inputs current to TERMINAL SI of the blower motor control relay in conformity with the required vent output. This current activates the blower motor control relay so that the current flows from TERMINAL M+ of the blower motor control relay to TERMINAL 2 of the blower motor to TERMINAL 1 to TERMINAL M- of the blower motor control relay to TERMINAL GND to GROUND, activating the blower motor. The blower motor then operates at different steps in conformity with variable current flow output from TERMINAL BLW of the A/C control assembly to TERMINAL SI of the blower motor control relay.

2. OPERATION OF AIR INLET CONTROL SERVO MOTOR
(Switching from FRESH to RECIRC)
With ignition SW turned ON, the current flows from HTR fuse (10 A) to TERMINAL IG of the A/C control assembly to TERMINAL MREC to TERMINAL 2 of the air inlet control servo motor to TERMINAL 6 to TERMINAL MFRS of the A/C control assembly to TERMINAL GND to GROUND, the motor rotates and the damper moves to the RECIRC side. When the damper operates with the A/C SW at RECIRC position, the DAMPER position signal is input from TERMINAL 5 of the servo motor to TERMINAL TPI of the ECU (Built into the A/C control assembly). As a result, the current to the servo motor circuit is cut off by the ECU, so the damper stops at that position.

(Switching from RECIRC to FRESH)
With ignition SW turned ON, when the RECIRC/FRESH SW is switched to the FRESH side, the current flows from TERMINAL IG of the A/C control assembly to TERMINAL MFRS to TERMINAL 2 of the air inlet control servo motor to TERMINAL 6 to TERMINAL MREC of the A/C control assembly to TERMINAL GND to GROUND, the motor rotates and the damper stops at that position.

3. OPERATION OF AIR VENT MODE CONTROL SERVO MOTOR
With ignition SW turned ON, the current flows from HTR fuse (10 A) to TERMINAL IG of the A/C control assembly.

(Switching from DEF to FACE)
The current flows from TERMINAL MFACE of the A/C control assembly to TERMINAL 4 of the air vent control servo motor to TERMINAL 5 to TERMINAL MDEF of the A/C control assembly to TERMINAL GND to GROUND. The motor rotates and the damper moves to the FACE side. When the damper operates with the A/C SW at FACE position, the DAMPER position signal is input from TERMINAL 1 of the servo motor to TERMINAL TPM of the ECU (Built into the A/C control assembly). As a result, the current to the servo motor circuit is cut off by the ECU, so the damper stops at that position.

(Switching from FACE to DEF)
The current flows from TERMINAL MDEF of the A/C control assembly to TERMINAL 5 of the air vent control servo motor to TERMINAL 4 to TERMINAL MFACE of the A/C control assembly to TERMINAL GND to GROUND, the motor rotates and the damper stops at that position.

4. OPERATION OF AIR MIX CONTROL SERVO MOTOR
When the temperature SW is turned to the "COOL" side, the current flows from TERMINAL MC of the A/C control assembly to TERMINAL 4 of the air mix control servo motor to TERMINAL 5 to TERMINAL MH of the A/C control assembly to TERMINAL GND to GROUND and the motor rotates. The damper opening angle at this time is input from TERMINAL 1 of the servo motor to TERMINAL TP of the A/C control assembly, this is used to determine the DAMPER STOP position and maintain the set temperature.
When the temperature control SW is turned to the "HOT" side, the current flows from TERMINAL MH of the A/C control assembly to TERMINAL 5 of the air mix control servo motor to TERMINAL 4 to TERMINAL MC of the A/C control assembly to TERMINAL GND to GROUND, rotating the motor in reverse and switching the damper from cool to hot side.

5. AIR CONDITIONING OPERATION
The A/C control assembly receives various signals i.e., the engine RPM from the igniter, outlet temperature signal from the A/C thermistor, coolant temperature from the engine coolant temp. sensor and the lock signal from the A/C compressor, etc. When the engine is started and the A/C SW is ON, a signal is input to the ECU (Built in the A/C control assembly). As a result, the ground circuit in the A/C control assembly is closed and current flows from HTR fuse (10 A) to TERMINAL 1 of the MG CLT relay to TERMINAL 2 to TERMINAL ACMG of the engine control module to TERMINAL A/C to TERMINAL MGC of the A/C control assembly to TERMINAL GND to GROUND, turning the relay ON, so that the A/C magnetic clutch is on and the A/C compressor operates.
At the same time, the engine control module detects the magnetic clutch is on and the A/C compressor operates. Open direction to avoid lowering the engine RPM during A/C operating.
When any of the following signals are input to the A/C control assembly, the control assembly operates to turn OFF the air conditioning.
* Engine RPM signal is high.
* Coolant high temp. signal is high.
* A signal that the temperature at the air outlet is low.
* A signal that there is a large difference between engine speed and compressor speed.
* A signal that the refrigerant pressure is abnormally high or low.