Does anyone have the hvac schematic for the control panel? (1990 2500)

[dudeinthepnw]

When I got the truck a few months ago, one issue it had was the radio wasn't working. I ordered a retro sound factory unit that still allowed me to have aux etc but also still look factory. I removed the factory stereo and the CMD (I think that's what it's called, the part under the dash that actually controls the radio head unit). Before doing so, the HVAC worked great, cold air, hot heat, functioned 100% - After pulling the radio out, it stopped working. It still lights up when I turn the lights on, but none of the functions work. I don't think it's an issue with the hvac control unit, I think I may have pulled something lose when removing the radio but I can't seem to find anything obvious. Because of this I haven't installed the new radio, want to fix the HVAC issue and then I'll install the new radio. From the bit of research I've done, I read that the wiring heads towards/behind the glove box, I pulled the glove box out and nothing seemed to be awry. I was also informed there is a grey connector behind the ashtray that plugs into the hvac unit, I thought this might be the likely culprit given the location. I found what I believe is the correct connector but it seems fine. And yes, the first thing I did was check fuses to make sure I didn't pop a fuse.

Any suggestion aside from the schematic request? I can tear down and re-assemble an engine, but electrical stuff has never been my cup of tea, especially when it comes to diagnosing. It would be really nice to get this solved - having the defroster working again would be nice. Being able to figure out this issue so I can install the radio would also be nice.

Naturally my hunch tells me I'm overlooking something simple, but we all know how these things work.

 

[DerekTheGreat]

Before tearing into that, I'd either unplug the HVAC control module or the battery, wait five minutes and then plug it back in and/or hook the batter back up. Sometimes they just need a reset.

If that doesn't work, swapping in a known, good HVAC head unit thing is what I'd try next.

 

[AK49BWL]

I would try unplugging and replugging the HVAC control head. It's possible the wires for the stereo head caught on the HVAC connector and pulled it loose. Or the pins are corroded just enough that good contact isn't being made.

 

[east302]

PDF scans of the factory manuals can be downloaded here. They should have the wiring diagrams and connector views

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

 

[dudeinthepnw]

Finally had a little time to figure it out this morning. Turned out to be one of the plugs that goes into the ignition switch on top of the steering column had pulled out. Made a quick video for anyone interested as I hadn't seen this as a solution posted anywhere.

xc_hide_links_from_guests_guests_error_hide_media