Compressor Control (740i/iL)

IHKA E32 COMPRESSOR CONTROL (740i/iL)







As introduced for 1993, the M60 740i/iL compressor control system is similar to that of the 1991 M50 525i (IHKR2); the engine control module is programmed with A/C compressor control logic and determines whether or not the compressor should operate.

V-8 compressor control is as follows:
- When the "snowflake" or recirculating air button is pressed, the IHKA control panel sends a compressor request signal to the IHKA control module.
- The IHKA control module passes the request on to the engine control module (ECM) via the compound pressure switch (mounted on the receiver/dryer). For pressure switch specifications, refer to Switch Values below.

- If refrigerant high-side pressure is too high or too low, the compressor request will not reach the ECM.
- If high-side pressure is within limits, the compressor request reaches the ECM. The ECM can then look at input data from other sensors and use it to stabilize engine speed and determine whether or not the compressor should operate.

- Under normal conditions, the ECM receives the compressor request signal and energizes the compressor control relay to provide power to the A/C compressor clutch.
- If, however; engine coolant temperature is too high, or "full load" conditions exist, the ECM will not energize the clutch.
- Full load is defined as wide-open throttle at a vehicle speed of 5 mph (8 kph) or less. Full load out-out lasts for a maximum of 8 seconds.

- If evaporator temperature falls too low, the IHKA control module stops sending the A/C compressor request to the ECM and the ECM de-energizes the compressor control relay.


NOTE: As of 8/92, the refrigerant system on 740i/iL vehicles was filled with R-134a.


Compressor Protection Pressure/Temperature Switch Values

HIGH PRESSURE SWITCH OPENS @ 441 psi (30 bar), PRESSURE INCREASING
CLOSES @ 338 psi (23 bar), PRESSURE DECREASING

LOW PRESSURE SWITCH * OPENS @ 17 psi (1.2 bar), PRESSURE DECREASING
CLOSES @ 32 psi (2.2 bar), PRESSURE INCREASING

COMPRESSOR HOUSING OPENS @ 266 OF (130 °C), TEMP INCREASING
TEMPERATURE SWITCH

* The Low Pressure Switch is used to sense low pressure on the HIGH side of the refrigerant system.


NOTE: As of 3/92, the refrigerant system on 735i/iL vehicles was filled with R-134a.