when I went on the ill fated maiden voyage, I had the AC on and running. In removing all sorts of jiggery pokery from the engine that the PO installed, I'm fairly certain that I removed some crucial unknown wire that allowed the system to work, because now it's not blowing. at all. No heat either.

The only thing I get is a thumping sound behind the passenger side of the dash when I put on the hi setting. from what i understand, the hi setting comes from a different system than the others? How does that work?

I'm 90% certain that one of the switches that the PO installed had something to do with the hi setting on the AC, and that's the only way I had it running because, well....Texas.

I did notice that when I had it on yesterday while running the coach just to warm it up and keep things moving, the AC compressor got cold. so something is working, perhaps just the blower motor is not?

Atom Ant wrote on Wed, 23 November 2016 16:23

when I went on the ill fated maiden voyage, I had the AC on and running. In removing all sorts of jiggery pokery from the engine that the PO installed, I'm fairly certain that I removed some crucial unknown wire that allowed the system to work, because now it's not blowing. at all. No heat either.

The only thing I get is a thumping sound behind the passenger side of the dash when I put on the hi setting. from what i understand, the hi setting comes from a different system than the others? How does that work?

I'm 90% certain that one of the switches that the PO installed had something to do with the hi setting on the AC, and that's the only way I had it running because, well....Texas.

I did notice that when I had it on yesterday while running the coach just to warm it up and keep things moving, the AC compressor got cold. so something is working, perhaps just the blower motor is not?

Seems to me the only thing that can thump is the fan.

My guess is there is not enough power getting to the blower motor on any setting except high, and when it gets enough power, it beats against a rodent nest. If the compressor is getting cold, the blower motor fuse is OK. You will probably need to take the motor out/off anyway to untangle the fodder in the blower box.

And check the wiring diagrams at http://www.gmcmhphotos.com/photos/hvac-dash-and-blower-control/p58076-78-hvac-control.html or at http://www.gmcmhphotos.com/photos/electrical/p50601-high-speed-dash-fan-circuit-path.html depending on which dash fan control you have (low/medlow/med/hi or off/lo/med/high).

Atom Ant wrote on Wed, 23 November 2016 18:11

I think he is trying to catch up with JimK.
Matt

Answers to the post that has writing in it.

There are only three things that can "thump" in and about the right side dashboard. The fan would be my first guess, too. If the compressor is running and you aren't getting any cool air out, then the fan would be a good place to start. It is not hard to remove and yes, little animals like to make a home in GMCs. (I think they know that they will be around longer than Winyboxos.) If the thumps was real regular, that is almost a given. If the thump was slow and irregular, then it might be one of the HVAC doors opening and closing as it tried to do what the control wanted and there is a vacuum leak so it sets up an oscillation.

Good luck

Matt

The thump is a single sound, as a reaction to setting the switch to the hi setting.

The blower is grounded with a single black wire under one of its mounting
screws. That screw is threaded into the fiberglass housing. If even
slightly loose, it will disable the fan.

Put a star washer and anti-corrosion compound on it and tighten it securely
-- with a larger screen if necessary.

Ken H

So why didn't you suggest fastening it with something besides a "screen"?

Ken H