heat and air control

[91chevystumped]

I have a situation maybe some of you can help. My 1991 K1500 4x4 would not light up or operate the heating controls this morning. I drive the truck every day and when I parked it last night it was working fine. I have checked all fuses and they are good. I have taken the old control box out and tried two different ones at a local junkyard today and they didn't work either. The plug into the back of the box shows 12 volts on a volt meter up to that point. I have both a Haynes and a Chilton repair manual; one says I should have a "maxi-fuse box" under the hood and I don't; and the other says I should have an old school slide control for my heater and I don't. The schematics are different in both books also; and neither seems to be in line with the truck. What in the world has happened to my heater?

[mudseeker]

first off, those books go from 88 to 98 so that would explain all the mis-information. your truck has the little control box next to the dash cluster right?

[91chevystumped]

Yes, it does have the little control box with the digital display.

[mudseeker]

i'll take a look at my book in the afternoon.

[91chevystumped]

Thank you mudseeker for your assistance. This morning I got my handy dandy testing device and took the rest of my dash apart and started checking wires for continuity and discovered a plastic clip that was burnt almost in half causing the hot all the time wires to not connect before the three relays behind the glove box. Touched them together and everything came on and worked, so I removed the plastic thing and spliced all the wires together appropriately and all is good now. Maybe someone will be able to use this post at sometime in the future. I will check back every couple days maybe I will be able to help someone some day. If your book says this plastic thing is required please let me know and I will get one.

[mudseeker]

could you describe what it looks like or get a picture of it?

[91chevystumped]

It appears to be just some sort of connecting device; it does not have a fuse or anything like that in it. I just wire nutted the wires together and everythign seems to be alright as I drove it over a hundred miles to go snowboarding today. Thanks anyway

[crabtruck]

Sounds like the red wire that comes from the firewall and fusible link (1 from connector spliced to 3 outputs).
But that doesn't go to all the relays if I have it right, just the low relay, the "B" resistor and
the a/c controller main power input, which would explain no display lights.
The brown wires (1 from connector spliced to 6 outputs) going to all the relays for blower, the a/c clutch relay (two)
and the key input of the controller (which would also explain no display) run off the 25A heater fuse.
Glad to hear you found it and it's good now.