Heating and Air Conditioning: Description and Operation

System Outline

1. Heater Blower Operation
When the blower speed is set to a certain level using the blower control SW, the A/C control assembly sends the signals to the blower control to control the blower motor speed.

2. Damper Servo Motor (Air Inlet) Control
When the FRESH/RECIRC select SW is set to RECIRC, the motor in the damper servo motor (Air inlet) starts rotating to move the damper toward the RECIRC side. Since the damper position is detected by the TERMINAL REC of the A/C control assembly, the motor is continuously rotated until the damper reaches its stop position.When the FRESH/RECIRC select SW is set to FRESH, the motor in the air inlet control servo motor starts rotating to move the damper toward the FRESH side. Since the damper position is detected by the TERMINAL FRS of the A/C control assembly, the motor is continuously rotated until the damper reaches its stop position.

3. Damper Servo Motor (Air Vent Mode) Control
When the mode select SW is pushed, the ECU in the A/C control assembly activates the damper servo motor (Air vent mode). This causes the servo motor to rotate to the position (FACE, BI-LEVEL, FOOT, FOOT/DEF, DEF) selected using the mode select SW, and moves the damper.

4. Damper Servo Motor (Air Mix) Control
When the temperature control SW is pressed, the ECU in the A/C control assembly sends a signal to the damper servo motor (Air mix). This signal drives the motor to reach the temperature set by the temperature control SW, and moves the damper.

5. Air Conditioning Operation
The A/C control assembly receives various signals, I.E., the engine RPM from the engine control module, out side air temperature signal from the ambient temp. sensor and coolant temperature from the engine control module, etc. When the engine is started and the A/C SW (A/C control assembly) is on, a signal is input to the engine control module. As a result, the ground circuit in engine control module is closed and current flows from ECU-IG fuse to TERMINAL 1 of the MG/C relay to TERMINAL 2 to TERMINAL ACMG of the engine control module, turning the MG/C relay on, so that the magnetic clutch is on and the A/C compressor operates.

At the same time, the A/C control assembly detects the magnetic clutch is on and the A/C compressor operates. If the A/C control assembly detects the following conditions, it stops the air conditioning:
- Evaporator outlet air is too low.
- There is a marked difference between the compressor speed and the engine speed.
- The refrigerant pressure is abnormally high or abnormally low.
- The engine speed is too low.
- Rapid acceleration occurs.

6. DEF Synchronized Control Function
When the blower SW is on and the air vent mode control SW turned to DEF or FOOT DEF position, if causes A/C to run whether A/C SW is on or not.