Noise from rear HVAC? [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: Noise from rear HVAC?

11-07-2006, 06:58 PM
I have a 2004 Trailblazer EXT. This morning, it started making a clunking/knocking noise in the right rear, inside. I'm pretty sure its from the area of the rear HVAC unit, which I confirmed by fiddling with the front console mounted rear HVAC switch. I could get the noise to stop by moving the switch to "R". The noise would stay stopped if I moved it back to "0", but if I moved it to any other position (1-3) it would return.

Anyone else have this problem? Any thoughts on it? I'm hoping it's nothing major, since I'm just outside of warranty (38k miles)

-Tony Z

11-07-2006, 08:33 PM
Does it do it with AC both on & off? If so, I would say it is the fan, if only with the AC on it, I say it is the rear compressor. But, these are just guesses. If you are still within the time frame of warranty or at least close, since you are just barely over on miles I would go to the dealership and talk to them. I know GM has fixed the AC on Mom's '96 Beretta several times after the warranty expired.

11-07-2006, 09:09 PM
Sounds like the rear fan to me. The "O" position on the consol switch has turned off the rear fan. The 1 2 3 of course are fan speeds. The "R" position passes control to the rear switch (which must be off). I would say you have a bad fan motor or something touching the fan blade. Mine is working ok, so I cann't help with hands on getting at the fan, sorry.

11-07-2006, 09:17 PM
That's the weird thing, I could swear that the rear controls were not off, and if I turned the front control to 0, the noise didn't stop- I had to turn it past 0 to R (which was not set to off). Now that I think about it, the other day I commented to my wife that the switch was goofy- sometimes it wouldn't change properly from one speed to the next (say 1 to 2 or vice versa) with a casual turn of the knob. I had to really make sure it was in the notch, even go past it and come back to get it to register and change to the right speed. I'm starting to wonder if the switch is wonky too, besides the noisy fan/unit.

Thanks for the feedback. I'll do some more troubleshooting tomorrow and post more info if I learn anything.


11-07-2006, 11:08 PM
I have a weird sound coming from the rear HVAC unit in my SWB, sounds like the fan is failing?

11-09-2006, 10:53 AM
Looks like my initial observation was correct. The noise occurs with the front control set on 1-3, does not stop when set to '0', but will stop when switched to 'R' (and remain stopped if switched from 'R' back to '0'), even with the rear controls set to 'on'. Really weird. I guess I'll have to pull the interior panels out and see what's really going on.


AJ Kent
11-26-2006, 09:49 PM
I have the exact same problem with my Envoy! What ever happened? My noise seems to happen periodically. Tonight it would not make noise, but tomorrow it may start again. It's the right rear passenger side and it knocks or bangs. Can shut it down by turning the rear blower motor switch to R! I would appreciate any help you can give me.

AJ Kent
11-28-2006, 08:51 AM
I have not been able to obtain an answer to the problem. Would someone who has 10 posts or more send an email to member "zielinab" and inquire as to what they found was the cause of the problem. I understand that you need to have rules for the forum, but this is one instance where it hinders honest folks!

Peace, AJ