Quote:
Originally Posted by rwdkev
Dave,
On cars with fuel injection, ECU takes signal from A/C control unit (and in some cases also compressor clutch feed) and uses this to adjust Idle Air Control (IAC) valve.
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Very true Kev - it also brings the secondary cooling fan into play as well. That fan is mainly to cool the evaporator but helps cool the engine and there is an override where the electric fan comes on as well if the standard vicious coupled fan isn't coping.
I'd have to check on the Volvo diagram but on my other beast, the battery voltage can also cause the ECU to increase the idle speed, if the ECU senses the battery voltage is low, for example if the headlights, HRW, heater fan and so on are all operating and the car has just been idling for a period, say on the M25 in rush hour.
As an aside - rush hour, when the traffic moves at its slowest!
