[Solved] Hvac fan not turning on at all (1995 chevrolet k2500 7.4 tbi)

[Cuckfield]

1995 chevrolet k2500 7.4l
Hello, my hvac one day just completely stopped working.
Replaced relay, resistor, and blower motor, stopping and testing each tome after replacing a part, and no dice. What else could there be?
Might it be the switches? If it is the switches, how can I check? The lights for recirc and a/c light up when I press them. Power is coming to the little light in the top left of the switches that lights up when you turn on the headlights.
I know that the only way to replace the switch assembly is to buy a '96 one and put an adaptor harness in, anyone done this?

 

[GoToGuy]

HVAC is the whole system. We can't see or hear what you do? So you you have describe what's going on or not working? HVAC stopped , that dog don't hunt. What specifically do you need help with? What does stopped working mean? No blower fan in any position, hi, med, etc? AC selected not getting cold? Instrument lighting is separate, headlight system.
Did you do any diagnostics. Check fuses? Or just start tossing parts at it?

 

[Cuckfield]

HVAC is the whole system. We can't see or hear what you do? So you you have describe what's going on or not working? HVAC stopped , that dog don't hunt. What specifically do you need help with? What does stopped working mean? No blower fan in any position, hi, med, etc? AC selected not getting cold? Instrument lighting is separate, headlight system.
Did you do any diagnostics. Check fuses? Or just start tossing parts at it?

No blower fan in any position. Checked fuses, all look fine.
Ac is dead, but that's a different hoss. My ac system has a leak and the compressor kills it with the low pressure switch when I turn it on.

 

[GoToGuy]

Nope, once the low pressure switch opens,from the leak, it stays open until the system has been serviced to at least 30 psi. The circuit stays open, no power to compressor, regardless of control switch positions.

 

[Cuckfield]

Nope, once the low pressure switch opens,from the leak, it stays open until the system has been serviced to at least 30 psi. The circuit stays open, no power to compressor, regardless of control switch positions.

Evidently I'm operating on bad info. That aside, any way I can test my hvac control switches?
Pulled the switch module out and the connectors look fine to the eye.

 

[PAIRA90S]

On both my 90 Chevy & the GMC, the harness needed to be pressed in firmly. The one that gets stressed during an aftermarket stereo install. It would be fine for a while then I'd lose various controls. Ended up using a small plastic wire tie wrapped around the harness connection, the bundle, not into the HVAC, to hold the plugs tighter. Pretty much squeeze it together by hand to check. Yeah, mine looked all good to the eye too and was clipped at the lock tab but... Works with no further issues

 

[Scooterwrench]

Download the FSM in the sticky at the top of this forum then follow the service procedures. There are relays that control blower speed, may be one of those is bad. Unless you want to spend money replacing parts it doesn't need follow the service procedures and diagnose it correctly.

 

[Erik the Awful]

No blower fan in any position. Checked fuses, all look fine.

Put a test light across the fan connector terminals. If the test light lights, your fan is bad.

If the test light doesn't light, check from the power side of the terminal to ground. If you don't have power, work backwards along the circuit until you find where you lose power. If you do have power, your ground is bad.

 

[Cuckfield]

Put a test light across the fan connector terminals. If the test light lights, your fan is bad.

If the test light doesn't light, check from the power side of the terminal to ground. If you don't have power, work backwards along the circuit until you find where you lose power. If you do have power, your ground is bad.

Can I use a multimeter for this? If I can, how? Sorry for dumb questions. Never done much electrical stuff.
Also, by fan connector terminals you mean the prongs on the fan that you connect the harness to, right?

 

[Cuckfield]

Figured it out, gentlemen!
Underneath the dash there is a red and black wire joined together with a plastic connector. I pulled them apart, and the ground wire terminal on it is melted and shredded!

Armed with that knowledge, I kicked on the key and wiggled the wires. When I wiggled them a little bit, the relay started clicking. When I wiggled them just right, the blower turned on! When I could hold it just right, I tried every speed. Every speed works as intended when the connection is just right.

I'm gonna just splice together the wires with a butt crimp and wrap them in electrical tape and call it good.