C5 mk1 Air con question?

[waynedance]

Is there any sort of sensor on the aircon system that adjusts the engine revs?

Reason I ask is that the engine seems to run lumpy with air con switched on, maybe imagining it!!!

[spider]

General info not C5 specific not sure if its any help:

The pressure sensor in the pipework or just the fact the AC compressor clutch is enabled and the engine is running (as its done via the BSi anyway I suspect) would be enough to signal the engine ECU to increase idle speed slightly. Not dissimilar to how some cars have a power steering switch fitted so when its on or approaching full lock it will increase the idle speed.

This would just be to make up for the otherwise apparent drop in idle speed to compensate for the loading of the compressor.

In theory it should idle at the same speed though as the 'higher!' signal is just so it stays the same.

Probably more apparent with a petrol engine though as their torque is a bit higher up the rev range so may suffer a bit more from an idle drop compared to a derv unit generally, I just mean by this its generally quite difficult to accidentally stall a diesel engine compared to a petrol unit that's all.

[waynedance]

Yeah helps a little, I was thinking there maybe a switch like in the power steering but as you said maybe BSI controlled.

[SaabC5]

Generally when the compressor cuts in the revs drop a little and the cars electronics notice this and increases the rpm to counteract the drop. Its generally more noticeable in smaller engines with a/c, my 1.6 Laguna dropped 150rpm and then picked up again. The 2.2 Citroen i don't notice any discernable drop in engine revs when it cuts in.