RPMs and fan???

[nomi123]

Recently my RPMs have been fluctuating by about 200 while driving, in park while idling, and at a complete stop in drive. I have been able to make this change reproduce itself when I turn on the heater fan or the AC. Otherwise, it runs perfectly fine.

Any ideas on what may be causing this fluctuation while the fan is running? It sounds like something is turning on and off (there is no change in the force of the heat or AC when it does this).

Naomi

[busboy4]

Hi Naomi

If your A/C is on, I would find this normal, especially in cooler weather as the A/C compressor clutch will cycle on and off at a faster rate than if the outside temp is hotter. The on off you are hearing: is it from the right front of the engine compartment? Sounds like a loud click? That would be your A/C compressor. The rapidity of cycling should be related to outside temperature as I indicated before. If in warm weather you are still seeing rapid cycling, you might have other issues - low freon charge chiefly - and would also notice poor A/C performance.

Hope that helps

[nomi123]

Thanks, I'll watch and see what it does as the weater warms up. It also does this change in RPMs when the heater fan is on. Are they related or is this a different issue?

Naomi

[busboy4]

Hi Naomi
if by heater fan you mean your interior fan, then no, the two should not be directly related. However, the A/C runs on settings other than just A/C. Defrost for instance, also starts the A/C. Take a look at your owners manual. You may be getting the A/C compressor running when you did not expect too?

I would go this far: if you select floor heat only, and select a comfortable fan setting you should not get A/C. Do you experience the rpm fluctuation in this configuration?

[jgattian]

Originally Posted by nomi123

Thanks, I'll watch and see what it does as the weater warms up. It also does this change in RPMs when the heater fan is on. Are they related or is this a different issue?

Naomi

With the A/C on or the heater in defrost mode which both use the A/C compressor the computer ups the engine idle speed to compensate for the increased engine load to prevent the engine from dying or stalling.

So yes if you are sitting at idle and turn on the A/C the enging RPM's will increase.