AC stopped working

[TC233]

1991 GMC Sierra 1500- Checked the manual and it said the AC/HTR and the 4WD lights on the floor console are on the same fuse.
So I put it in 4WD and sure enough the light does not come on. I bought the truck 3 days ago and I ensured light worked then. So I know the lights work. So its obviously the 25 AMP fuse in the panel, right? Wrong? Fuse is good. So the question is, where does the power come from that supplies the fuse?
I assume its the block on the firewall with a number of "clips on it"
Just have no idea where to start.
I have ordered a shop manual, but I think it will take at least a week to get here, meanwhile I am frying in the heat! Any idea where to check next?

 

[rdm1465]

you seem knowledgeable about how things work, and willing to make adaptions.

so here is my probably useless thoughts. there is so little that could go wrong with AC. Based on what you said, I am guessing you also checked that the belt is on the AC. Could be a bad switch, or really hope not a bad compressor.

 

[Pal]

I have the same problem on my '98 Sierra, so I'm wondering if you ever found the solution.

 

[dirtclod]

Your a/c problem may not be linked to the 4wd light. Possibly the light bulb or connection has failed. With engine running and a/c switched on, disconnect electrical plug at accumulator and check for power. If no voltage there, then go to fuses. If power is at accumulator connection, then go to compressor connection and check power. You won't need a book to check these. Clip neg (-) testor lead to battery (-), and check each connector wire. There are 2 wires at each one. One of them should show voltage.

 

[Bill325]

If your truck uses the same AC electrical controls as my lady friend's 2003 Chevy Malibu, then you can attribute the malfunctions to an electrical gremlin we call " Sparky", commonly found in GM vehicles of these years. Sparky allows your AC to operate/shut down whenever he feels like it , as well as activating the theft deterent system that prevents us from starting our own car. Sparky also activates various beepers and warning lights in the dash, locks us out of the car , makes the CD player erratic, and otherwise controls the electricals of the vehicle . After totaling her first 2003 Malibu in an accident, she bought a second identical one. We thought the second car would not come with the same electrical problems. We were wrong. Different Sparky, exact same problems.