Compressor Control

IHKR2 COMPRESSOR CONTROL







- On the 1991 525i, when the A/C system is turned on, the IHKR control module sends the A/C request to the engine control module.
- The pressure switch is in the middle of this circuit. If refrigerant pressure is within limits, the request signal reaches the engine control module.
- The engine control module uses data from its engine control sensors to determine whether to turn on the A/C compressor (by grounding the compressor control relay).
- The engine control module won't turn on the A/C compressor if coolant temperature is too high, or during wide open throttle conditions.
- If evaporator temperature falls too low, the control module stops sending an A/C request signal to the engine control module.
- The engine control module then turns off the A/C compressor clutch.