HVAC Compressor Controls Circuit Description. Pontiac Sun Runner - 4WD (Canada) 1998

For 1990-2009 cars

The A/C compressor control module is powered by the voltage from the heater fuse and is permanently grounded at G202.

An , through the blower speed selector switch and the A/C switch,

With the ignition switch, and the A/C switch in the ON position, and the blower speed selector switch in any position except OFF, an A/C request signal is applied to the A/C compressor control module through the blower speed selector switch and the A/C switch. This prompts the A/C compressor control module to supply the powertrain control module (PCM) with an idle-up signal.

The refrigerant pressure switch closes when the pressure in the A/C system is between 193 kPa (28 psi) and 3137 kPa (455 psi). Voltage is then provided to the A/C compressor clutch relay coil.

Whenever the pressure in the A/C system drops below 193 kPa (28 psi) or rises above 3137 kPa (455 psi), the refrigerant pressure switch opens, the A/C compressor clutch relay will de-energizes and voltage to the A/C compressor clutch is interrupted.

These conditions only occur under extreme circumstances or when a fault is present, such as a low refrigerant change or an improper evaporator temperature.

The engine coolant temperature (ECT) sensor opens when the engine coolant temperature rises to above 113°C (235°F). This signal warns the A/C compressor control module that the engine is overheating, prompting the A/C compressor control module to disengage the A/C compressor clutch in order to reduce the engine load.

The A/C compressor clutch relay coil is grounded through the A/C compressor control module at G202, provided that the A/C compressor control module has not received a low temperature signal from the evaporator temperature sensor, a high temperature signal from the engine coolant temperature (ECT) sensor and the refrigerant pressure switch is closed.

When the relay is energized through the refrigerant pressure switch, battery voltage is applied to the A/C compressor clutch through the A/C fuse and the contacts of the A/C compressor clutch relay. Since the A/C compressor clutch is permanently grounded, the clutch engages and the compressor operates

The A/C compressor control module monitors the evaporator temperature sensor that is mounted on the inside of the evaporator housing. The evaporator temperature sensor converts evaporator core temperature into a resistance value. Using this resistance value, the A/C compressor control module can sense when the evaporator temperature drops below 0°C (32°F). This causes the A/C compressor control module to remove the A/C compressor clutch relay coil ground. This prevents any evaporator frost or ice build-up which reduces airflow and the cooling capacity of the unit.

The A/C compressor control module provides a signal to the powertrain control module (PCM). The PCM uses the signal in order to increase the engine idle when the A/C system is active. If the A/C system is off, the PCM controls the engine idle according to other inputs.