I have an 04 and the AC has literally started making a screaming sound sometimes. The sound is coming from the rear of the vehicle, assuming its the rear AC unit (?).. Front and rear AC's are cold, but I have to turn the AC off completely to get the noise to stop. Turn the AC back on and it will work normally for some time.

really odd and intermittent issues are hard to figure out.

Any ideas??

 

When you "Turn the A/C off completely", do you mean that you also shut the rear fan off? If so, when it starts screaming again, leave all settings where they are and move the rear temp from cool to heat and see if it stays screaming. If it does, then it would be the rear fan motor as it's the only moving part in the rear other than the HEAT/COOL damper.

 

Ill give it a shot..

It takes me shutting everything off Fans/AC etc. in order to get it to stop.. Just shutting the rear off doesnt have an effect.

 

slowly going to cool-hot didnt stop it.

 

Just trying to help here. So I'm not missing anything, what happens if...

1. You leave everything on when it starts screaming and just turn the A/C compressor off?

2. You leave everything on when it starts screaming and just turn the rear fan off?

3. Does the sound change with the speed of the fan?

 

No it doesnt change with the speed of the fan...

Interesting enough, playing around with it yesterday. The tone seems to be tied to the accelerator. when I let off the gas it changes pitch.

When this happened I slowly turned it to warm and it stopped.. Here is a video... you can hear the tone change when I let off the gas then it stops when I turn to warm... (Sorry but my wife is on the phone during this)

 

That is weird. If it was me, my next step would be to remove the left rear panel and have my wife drive the vehicle while I parked my carcass in the back waiting for the noise. Then when it starts, locate the source with my ears and hands.

 

^ yep that is my next plan of action... The unfortunate part is its so sporadic it will mean a lot of miles in the back. At this point I'm thinking it's something with the lines or rear housing itself...

 

I got to thinking on the way home Friday that it could be your expansion valve for the rear A/C whistling. Never heard one do it before, but then one never knows.