Control Module HVAC: Description and Operation

Compressor Control System

1. SCHEMATIC

Wiring Diagram:

1. When the A/C switch and fan switch are turned ON, the A/C relay activates. The compressor and F.I.C.D. are turned on, and then the main and sub fans also operate. Blower relay operates to direct the air flowrate determined by FAN switch position.
2. The thermo amplifier activates to stop the compressor clutch, F.I.C.D., and main and sub fans.
3. When the "High-Low" pressure switch operates, the compressor clutch and F.I.C.D. stop but the main and sub fans are operating.
4. When the fan control switch operates, both the main and sub fans operate




2. THERMO CONTROL AMPLIFIER
The thermo control amplifier disconnects the magnet clutch circuit to prevent the evaporator from becoming frosted when the temperature of the evaporator fin drops close to "2 °C (36 °F)". As the evaporator is cooled, the thermistor (located on the evaporator fin) interrupts the "base" current of the amplifier. This in turn deenergizes the A/C relay coil, which in turn disconnects the magnet clutch circuit.




3. ACCELERATION CUT SYSTEM
The A/C switch turns the A/C system on or off. The on-off operation of the switch is transmitted to the ECU.

The A/C cut relay breaks the current flow to the compressor, through the use of an output signal from the ECU, for a certain period of time when a "full-throttle" signal (emitted from the throttle sensor) enters the ECU while the compressor is operating. This prevents the degradation of acceleration performance and stabilizes the main fuse box located on the left side of the engine compartment.




4. F.I.C.D.
The F.I.C.D. increases engine idle speed when the compressor is turned ON.

The Engine Control unit activates the by-pass air control solenoid valve in advance to control the amount of by-pass air flowing through the throttle body in relation to the signal emitted from the A/C switch so that the proper idle speed specified for each engine load is achieved.




5. FAN CONTROL
The main fan and sub fan are switched between two stages, Hi and Low, according to the operating modes shown in the table.