rami

what supose to be the rpm number?
mine is 700 is that normal ? because i feel it too much
please tell me what u think?

znod

700 with AC on and 500 with climate control off--on my car. I am not sure what happens with AC off and heat on since I haven't used heat yet.

Rudy

Heat shouldn't affect RPM's in any way...

dgjk

0 when car off
700 when warmed up
most cars runs a little faster when cold - about 1200

znod

That's what I would think, but my understanding is that the compressor still is on some of the time so???

Rudy

Sure, but again, it has nothing to do with heat. In other words, the RPMs at idle can be one thing with the climate control system off and it can be something else with climate control on. The compressor will cycle on and off regardless of temperature settings (heat or cool).

I guess another way to say what I'm saying is there's one RPM speed for times when the compressor is on and one for when the compressor is off. The compressor may or may not be running when you have heat on -- the only way to turn off the compressor for sure is to manually turn it off.

All that said, I haven't looked at the actual RPM's with and without the compressor running so unfortunately I can't answer the original question yet. Keep in mind that on some cars, the idle is bumped up when the compressor is on to compensate for the additional load on the engine...

my530i

Rear defroster would drive down the RPM, not the heater.

znod

Right, from what I have observed, the idle is bumped up at least when the AC and compressor are on--whether the compressor is running big-time or not. In this reard, my further understanding is that our compressors do not acutally have a clutch; thus, they are on usually, to at least some minimal extent, whenever the light is on. My RPM is at 700 under these conditions. And, I do know that my RPM is 500 with climate control off.

And, as you say, the bump might coincide simply with climate control being on. And, this simultaneity might occur because of the way the compressors work. I'll check it out one day soon with climate control on and heat being emitted.