Air Conditioning Help...85 GMC

[chargedstang89]

Hello all....I'm kinda new here, so any help would be great. The A/C system in my 85 sierra is complete trash. I want to replace it, but I cannot find the wiring that should go to the compressor. The guy I bought the truck from was a moron. The wires hooking the accumulator and evaporator are there. I traced them last night, and they go into a wiring harness type thing that runs across the back side of the firewall. It ends almost in the middle of the firewall, and there is a flat, kind of square plug at the end of those wires. I'm thinking that there should be a wire that plugs into that and then goes to the compressor, but I'm not sure. The Chilton's manual doesn't show anything about the A/C, so I'm at a loss. Can anyone help???? If anyone could post pics of the wires, that would be awesome. Thanks...Josh

[bigd65]

i believe that is the plug that goes to the compressor. they should be GREEN wires, i believe. one lt green and one drk green

[chargedstang89]

I do believe I remember those being the colors. I will have to confirm tonight when I get home though. Do you know where I could find a picture of this?

[apstguy]

I maybe able to get you a pic tonight - the dark green goes to the compressor and the other wire grounds to the intake manifold.

[chargedstang89]

that would be so awesome if you could give me a pic. i'm in desperate need.

[apstguy]

Give me one minute...

[apstguy]

Just follow the green line...

[apstguy]

Hope that helps!

[chargedstang89]

thanks a bunch!!!! i'm going to print the pictures out and lay them side by side to trace the wire better. I am not sure what wire goes to the idle solenoid on the carbureator, though. Or am I mistaken? I'm under the impression that the darker wire grounds to the intake bolt, as described in the picture, and that the green wire goes to the compressor, but i'm not quite sure where the idle solenoid comes into play. AGain, that just comes from myself not understanding, as I'm used to cars having all their wiring already existing...haha I can't tell you how much I appreciate those pictures though.

[swervin ervin]

Great help Tyler.

The same wire that feeds the compressor, feeds the idle solenoid. If I remember correctly, it just splits with one going to the compressor and the other going to the solenoid. The way it works is anytime the compressor gets power. so does the solenoid.

[chargedstang89]

the only problem I see is that my carbureator is an edelbrock, not the original. i did get a quadrajet that is supposed to be the same as the original. it's the 1904 model. i'm not sure that the edelbrock has the idle solenoid on it. if it does not have it, what should i do? Sorry if that sounds dumb, but I'm used to fuel injection....i'm new to the whole carb deal.

[Slonaker]

You can buy one and add it to it. Since the 1904 is a quadrajet, you might be able to use a parts store or junkyard piece rather than having to shell out for an actual Edelbrock part.

Slonaker

[chargedstang89]

what exactly does that part do? sorry if that's dumb, but again, i'm used to fuel injection....lol

[apstguy]

It makes the idle speed a bit higher (normally 600 in drive, w/ac on it is 900) it keeps the engine from bogging down when the compressor kicks in. Swervin - I think the compressor and idle solenoid are on different wires because then I switch to A/C on the dash the idle goes up with the compressor spinning or not (when the high pressure switch turns it off). So I think it is different. I have two wires running that way - one to the compressor & one to the solenoid. I think the one to the solenoid comes from inside the cab on the HVAC controls.

[apstguy]

BTW, on the black plug to the compressor, under the duck tape (the original mesh like tape fell off) there is a resistor between the two wire coming out of the plug.

[apstguy]

Originally posted by chargedstang89
thanks a bunch!!!! i'm going to print the pictures out and lay them side by side to trace the wire better. I am not sure what wire goes to the idle solenoid on the carbureator, though. Or am I mistaken? I'm under the impression that the darker wire grounds to the intake bolt, as described in the picture, and that the green wire goes to the compressor, but i'm not quite sure where the idle solenoid comes into play. AGain, that just comes from myself not understanding, as I'm used to cars having all their wiring already existing...haha I can't tell you how much I appreciate those pictures though.

You couldn't see it in the picture, but the negative lead on the compressor is a lightish/dark blue (if that makes sense - like a dark baby blue) Only one wire runs TO the compressor the other to the solenoid.

[apstguy]

I have been doing some looking and I can't find any wiring diagrams for A/C at all! My Chiltons guide has no wiring for it whatsoever and very, very little info on A/C systems. Maybe go to your local Chevy dealer's parts department, get a nice guy to print out a diagram for you. I need to try that sometime.

[chargedstang89]

I know..the Chilton's shows nothing at all. If you look under the A/C components removal & installation section, they say they won't even show it to you b/c of risk of death or injury...what a crock. I may try splicing a wire to the solenoid (after i get one) and to the compressor off the same wire and see how that works. I bought my truck from a guy who completely hacked the wiring in it up. I've had to re-do everything so far. He had it hidden pretty well so I couldn't tell when I bought it. A new motor and a new transmission later.....the thing runs like a champ and 4x4 works great...so now I need to keep cool. Thanks for the help. If I have anymore problems, I'll breath some life back into this thread. Thanks again guys!!!!

JP

[79BIG10]

One thing you can do for a manual is get a factory shop manual for your year truck off Ebay. I got one cheap and it shows everything you might ever need.

[chargedstang89]

I'm trying to find the Idle Solenoid on Autozone's webiste, but I guess I don't know the proper name for it. Is that what I would tell them it would be under? I have noticed that it is not on my Edelbrock, but there are two threaded bolt holes on the driver's side of the carb that look like they mount something. I'm assuming this is where the solenoid would bolt in, and then it would have some type of arm that would extend out to push the throttle plate backwards when it gets power when I turn the A/C on. Is this correct?

Is this part called a fast idle solenoid, or idle solenoid, or idle relay, etc?

Josh

[apstguy]

fast idle solenoid I think. You don't really need it, but without it, it will bog the motor down everytime the compressor kicks in. If you have a 350, you probably won't need it. A 305 needs it (it is weak).