Aircon causing revs to drop too much while idling?

[MrPT]

Hi all,

I know that A/C places additional load on the engine, but recently I've noticed that the revs are dropping a little too much when the compressor kicks in. With the engine warm (so the idle point is 650-750rpm), I'll hear the relay "click" every few minutes and the revs will drop to ~500rpm. If stationary, the engine bogs down and the car shudders; if I'm pulling away and the timing is just right (wrong?!), I get a considerable hesitation but no misfire, lumpy running etc.

I know hesitation/rough idle can be caused by a number of things, but any thoughts re. the A/C scenario in particular? With the A/C off I don't have any problems, and in other respects the car is running smoothly. It's an N52, so no ICV to clean - maybe Vanos?

Rgds,

P.

 

[Player 1]

Your're right, it shouldn't drop that much.. You might have the beginnings of a seized compressor, with the engine and everything turned off, get hold of the compressor clutch on the front of the pulley and turn it (either way), it should have a little bit of resistance but ought to be fairly smooth to turn, some compressors might want to spring back if there is high pressure in the system.
It's a bit difficult to describe how the compressor should feel over text but most working compressors feel similar so if you have access to another car with working A/C, try turning the compressor on that to see what it should be like.

The main thing though is that if the clutch is seriously difficult to turn or feels like it hits hard points as you turn it, then the compressor's probably on the way out and you'll want to fit a new one along with a receiver drier.

 

[MrPT]

Thanks - thought this thread had died but that is great info.