A/C Compressor Circuit

WARNING: This page is about a different car, the 1996 Saab 900 and 1995 Saab 900. However, it is still accessible from the selected car via links, so may be relevant.

The A/C compressor is always on in AUTO operating mode. When A/C system is on, the A/C-heater control panel sends a voltage signal to Integrated Central Electronics (ICE).

If coolant temperature does not exceed 259°F (126°C), the ICE sends a voltage signal to Engine Control Module (ECM) via the anti-frost thermostat. The ECM adjusts idle speed, and after a short delay, sends a ground signal to the A/C relay via the low pressure and high pressure monitor. When A/C relay operates, the A/C compressor clutch circuit is completed. The ECM opens the circuit to the A/C relay under heavy acceleration.

In AUTO mode, during normal driving conditions and when outside temperature is above 33.8°F (1°C), the anti-frost thermostat decides whether the A/C compressor is to run or not.

The A/C compressor runs, even when cooling is not required, to prevent the misting of the windshield in damp weather. The A/C compressor is shut off in ECON (economy) mode.