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Things that quit working aren't always caused by mechanical or electrical failure. My heater fan has been making terrible "muffled" noises for a couple of years when it was turned to the higher settings but the heat and cool has worked. Earlier this winter, one cold morning as I drove away from home I turned the heater to defrost and heard some delayed sounds of the heater changing functions. But I didn't get any defrosting and not much heat either. I could get some heat so I didn't mess with the controls, waiting for warm weather to work on it. The heat didn't seem to be getting any better either.
The information I found on the Internet indicated I had a bad blend door actuator but the "fix-it" manual doesn't mention it or where to find it.
I can find the part listed at all the parts dealers web sites. My manual does explain in some fashion how to dig into the heater; sound insulators, cluster bezel, etc. which I proceeded to remove today to disect the dash in order to "find" the elusive actuator. I got to the heater controls and radio and found nothing but plastic heater ducts so decided to reverse directions and wait for a better day to drop the steering and the dash.
I was back to the last part on the passenger side and decided to look up behind some electrical connectors again with my head on the floor,looking up. There is a vacuum actuator hiding up there and a rubber skirted door that was partly blocked open with cotton batting. Aha!:hissy:
The heater blower is on a manifold coming from the air conditioner chiller and goes through the firewall up against the right fender. I pulled the blower away from the manifold and the blower wheel had cotton in the fins and cotton was packed back in the heater duct. I had to remove the computer to get the blower out. It's a very tight fit. There was cotton packed into the box around the chiller and into the "mode" door in the heater. The cotton was packed solid from the end of the blower wheel to the door. Good reason the air conditioner wasn't working.
I don't know if it's mice or chipmonks. There are chipmonks around. They must be coming in through the fresh air cowl.
Anyway, I pulled all the cotton out and vacuumed everything. Put everything back together, reconnected the battery and replaced the air bag fuse. Started the engine and the cold air works, the heat works, the defrost works and the fan runs on high nice and smooth.:) So check for rodent nests before suspecting something broke. They like to build nests or store food in the air filter box, too. So put a screen over the air intake horn.
 

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2003 gmc envoy_slt
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Gotta love Mother Natures sense of humor.
 
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