Compressor Control

IHKR1 COMPRESSOR CONTROL







On early 1989 vehicles, pressing the snowflake or recirculating air button sends an A/C request signal to the compressor control unit. The compressor control unit then provides power to the A/C compressor clutch.

Three Normally Closed (NC) switches are placed, in series, in the clutch circuit:
- The high-pressure switch opens if refrigerant pressure in the receiver/dryer exceeds 441 psi (30 bar).
- The low-pressure switch opens if pressure drops below 17 psi (1.2 bar).
- The A/C compressor switch opens if the compressor housing temperature reaches 266 °F (130 °C).

All three switches must be closed for power to reach the compressor clutch.

The control module signals the compressor control unit to shut off the A/C compressor if the evaporator core temperature is so low that condensation might freeze on it.

During late 1989, the compressor control unit was replaced by a relay.







The M5 compressor control system has additional components and circuits to delay A/C compressor clutch activation following engine startup, and deactivate the clutch under certain engine operating conditions:
- The compressor is shut off if coolant temperature exceeds 240 °F (117 °C).
- The compressor is shut off during wide open throttle conditions.