For 1990-2009 cars

The air conditioning (A/C) compressor control module controls and monitors the A/C system operation. The A/C compressor control module monitors the A/C switch position. The A/C compressor control module monitors the refrigerant (evaporator) thermistor which is mounted inside the evaporator housing. The evaporator thermistor converts the evaporator temperature into a resistance value. Using the resistance value, the A/C compressor control module can sense when the evaporator temperature drops below 1°C (34°F). When the temperature drops below 1°C (34°F) the A/C compressor control module stops the A/C system operation. Stopping the A/C system operation prevents any evaporator frost and ice-up. Frost and the ice-up will decrease the airflow and the unit's cooling capacity. The A/C compressor control module also gives an idle-up signal to the powertrain control module (PCM).

With the ignition switch in the ON position, system voltage is applied:

1. Through the HEATER fuse
2. Through the blower speed selector switch
3. Through the A/C switch

to the A/C compressor control module when both switches are in the ON position. With the ignition switch in the ON position or the START position system voltage is applied to the A/C compressor control module through the IG-COIL fuse.

The refrigerant pressure switch monitors the A/C system pressure. The refrigerant pressure switch remains closed as long as the refrigerant pressure is between 196 kPa (28 psi) and 3137 kPa (455 psi). With the refrigerant pressure switch closed, voltage is applied to the A/C 1 relay (compressor clutch).

The A/C 1 relay (compressor clutch) is grounded through the A/C compressor control module to G201 when the following conditions occur:

• | The A/C compressor control module does not receive a low temperature signal from the evaporator thermistor.

• | The A/C compressor control module does not receive a high engine coolant temperature (ECT) signal from the powertrain control module (PCM).

When the A/C 1 relay (compressor clutch) is energized, voltage is applied:

1. Through the A/C fuse
2. Through the closed contacts of the A/C 1 relay (compressor clutch)
3. To the coil of the A/C 2 relay (condenser fan)
4. To the A/C compressor clutch

The A/C 2 relay (condenser fan) coil is permanently grounded at G102 and energizes as soon as voltage is applied from the closed contacts of the A/C 1 relay (compressor clutch).

The A/C condenser fan motor is permanently grounded at G103 and the fan operates as soon as voltage is applied from the closed contacts of the A/C 2 relay (condenser fan).