A/C Control System Components Description

Relay (Condenser Fan / Magnet Clutch)
A relay to operate the condenser fan motor and magnetic clutch. The motor continues operation as long as the air conditioner (compressor) is under operation.

Magnet Clutch
A device used, with the engine running, for operating the air conditioner only when needed, and controlled by the A/C amplifier.

Evaporator Thermistor
When the evaporative temperature of a refrigerant drops toss to 2.5 °C (36.5 °F) or below, the evaporator fins get stuck with frost or ice, reducing the airflow, lowering the cooling capacity. The thermistor is a sensor which is used to prevent this frosting or icing.
The thermistor installed to evaporator converts the evaporative temperature into a resistance value and send it to A/C amplifier.

Dual Pressure Switch
This switch sends A/C cut signal to A/C amplifier when the cycling refrigerant pressure drops due to refrigerant leakage, its amount being too little or too much.
The switch is installed at the receiver dryer.

A/C Amplifier
A/C amplifier is installed to the lower evaporator case.
It controls operation of the compressor magnet clutch and according to the signals from the sensors and ECM which detect the state of the engine and driving conditions.
Main system control functions are as follows (at A/C switch ON).

Magnet clutch delay control
0.12 second (Time since A/C signal is sent from A/C amplifier to ECM till A/C ON signal is sent back from ECM to A/C amplifier.)

A/C ON-OFF control (High refrigerant pressure)
above 3140 kPa (32 kg/sq.cm, 455 psi): A/C OFF
below 2550 kPa (26 kg/sq.cm, 370 psi): A/C ON

A/C ON-OFF control (Low refrigerant pressure)
below 196 kPa (2.0 kg/sq.cm, 28.4 psi): A/C OFF
above 226 kPa (2.3 kg/sq.cm, 32.7 psi): A/C ON

A/C condition (evaporative temperature and A/C and ECO switches) (A/C switch ON) below 2.5 °C (36.5 °F): A/C OFF
above 4.0 °C (39.2 °F): A/C ON

A/C condition (evaporative temperature and A/C and ECO switches) (ECO switch ON) below 8.0 °C (46.4 °F): A/C OFF
above 9.5 °C (49.1 °F): A/C ON

ECM
The A/C amplifier outputs A/C signal to ECM when A/C ON conditions are satisfied on the A/C amplifier side. (The air conditioning system does not turn ON in this state.) When ECM detects through the A/C signal that A/C ON conditions are satisfied on the A/C amplifier side, it uses the A/C signal as one of the factors to output A/C ON signal and to control condenser fan relay, idle air control valve and fuel injection respectively.

A/C condition (by engine coolant temperature)
above 110 °C (230 °F): A/C OFF
below 108 °C (226 °F): A/C ON

A/C condition (while engine cranking with starter ON)
A/C OFF

A/C condition (by engine speed) (for 1.6 liter model)
above 6600 r/min.: A/C OFF
below 6400 r/min.: A/C ON
above 700 r/min.: A/C ON
below 500 r/min.: A/C OFF

A/C condition (by engine speed) (for 1.8 liter model)
above 6400 r/min.: A/C OFF
below 5900 r/min.: A/C ON
above 700 r/min.: A/C ON
below 500 r/min.: A/C OFF

A/C condition (while accelerating rapidly (when throttle opened 80% within 3.5 seconds))
A/C OFF