Heater control went dark...and it's cold outside!!!!

[Randy Curran]

Well my '92 Chevy truck's thermostat (5.7) was stuck open so I replaced it. While doing so I noticed that someone had a ground run to one of the bolts. No idea why. So I put it back on. Well on the maiden voyage it was working fine when all of a sudden the heater control went dark, then came back and then went black again. I've checked the ground (again not sure what it's for) and even made a better ground for it. Nothing. I even checked the wiring to the back of the control and there was one broken wire which I fixed. Any ideas? Because no heat is going to suck!!!!!!!!!!!!!!!!!!!!

 

[someotherguy]

The grounds at the thermostat (and next to it on the intake) are unrelated to the AC/heat controls, but they are super important to be in top notch shape. They're for your engine sensors and fuel pump relay.

The usual problem spot for the 1988-1994 AC/heat controls is a power/ground connection in the general area of the blower motor. It's been years since I've had to mess with it but if I recall it's either a 2 pin or 3 pin connector. It's not exactly notorious for being problematic, but in the rare cases that 1988-1994 people have problems with their controls going out, it's usually in that connector.

By the way, the broken wire you fixed - did it look like it was intentionally cut? Maybe a light green wire (very vague memory here) - if so, someone cut that on purpose because of a service bulletin for the early trucks like your '92 where the AC would disable itself. The controls pay attention to how often the clutch cycles on the compressor and if it cycles too rapidly, it assumes your freon charge is low and disables the compressor, causing the A/C icon on the display to flash. Some of the trucks would erroneously trigger this code; cutting the wire was part of the "fix."

Richard

 

[Randy Curran]

Yes it was green and yes it looked cut on purpose. Thanks!

 

[Intimi88tr]

Are the dash lights dim?

 

[Randy Curran]

Nope. I am but not the dash lights.

Also where is the connector for the heater/blower? Would that cause the control to go out?

I drove it later with the lights on and the light for the heat/cold adjuster is still lit up so I assume that control is getting power. A local junkyard has a switch for $25 so I may go that route.

 

[someotherguy]

It's near the blower motor, passenger side of the interior behind the dash. Wish I had a pic for you but I don't...and I don't have a GMT400 here anymore to take one, or I would.

There's probably some floating around on the forum though as it's an area that some others have had to address.

The backlighting in the controls that is part of the regular dash/gauge lighting is a separate circuit, BTW.

Richard

 

[Randy Curran]

Thanks. I replaced the control unit since mine looked like someone tired to tear it apart. It didn't help but at least I know its not the problem. On to checking the plug.

It's suppose to be a high of 15 here next week and this weekend were suppose to get a bunch of snow. Why do I live in South Bend, IN?

 

[Randy Curran]

Well, I took the glove box out and made sure all the connections were tight and boom everything works! Thank you lord and thank you someotherguy. You rock sir!!!!!!!!!!!!!!!!!!!!!