2000 LE heater is causing engine idle issues

[diyer]

this has been a great car with no problems what so ever. However, today, the weirdest thing happened...

when the heater knob is on defrost, the engine idles way up to about 1500 rpms, then immediately drops below 700 rpms, acting like it's going to stall (but doesnt), it revs back up. the engine will stall if its in drive or reverse. when it's in park, it repeats this idle up and down process over and over, unless you turn the heater knob to a different setting (other than the two defrost positions).


this is the first thing to go wrong with this car since it was new...has anyone else experienced this happening to them? please help. a bad switch? a relay? a short? what is causing this?

[AlaricD]

Originally Posted by diyer

when the heater knob is on defrost, the engine idles way up to about 1500 rpms, then immediately drops below 700 rpms, acting like it's going to stall (but doesnt), it revs back up. the engine will stall if its in drive or reverse. when it's in park, it repeats this idle up and down process over and over, unless you turn the heater knob to a different setting (other than the two defrost positions).

Put the heater on a vent position, then turn on the A/C. I expect you'll experience the same problem. Essentially, using the defrost position activates the A/C to dehumidify the air and speed defogging the interior glass.

Maybe the compressor is going bad or there's too much refrigerant/too high pressure.

[diyer]

thank you so much for the response. a/c is one area i dont do well in...and something i would not have looked at in regards to the heater. that being said, after doing what you suggested, this is what i discovered...

it is 28 degress outside...
when the car is cold, there is no problem
when the car is hot, is when the problem occurs.
(it just started yesterday...and why would it not do it when the car is cold vrs when its hot?)

and yes, when the heater knob is in a vent position (other than defrost), with the a/c on, it does the same thing, however, after watching the compressor during this erratic idle, its obvious the compressor is locked up (and the car is doing what its supposed to do, trying to keep the engine running).

its winter...is there anyway to disconnect the compressor "without" screwing anything electrical up? and if so, will the defrost still work? (not to mention we dont have the funds right now to replace the compressor and have the system refilled).

[AlaricD]

When it's cold enough outside, the A/C compressor won't come on (this is by design to prevent components from icing or some such).

I've found no way to de-link the A/C from the defroster. You could just pull the A/C fuse or something.