'95 c1500 A/C help please

Hi!

With the ignition on and fan set to low, change the output selector. Do you hear any soft clicking or whirring noises? Something may be stuck.

Does the A/C work? Have you verified that it is charged? Maybe it sounds stupid to suggest this, but with a truck that old...who knows for sure?

On a 1994 C1500, the A/C light will come on and the controller appears to activate a relay even though all the refrigerant is long gone from the system. The compressor does not run. Perhaps that was changed for '95.

I would check to see if you can hear the actuators running. Many of them are little stepper motors and they can get stuck. Any clicking or popping noises indicate mechanical trouble. Soft whirring would be the normal sound, but if takes too long, a gear may be stripped out.

You might also try disconnecting the battery for a little while, especially if you did the replacement with the electrical system "live" at the time. Perhaps the system controller is confused.

William

Thanks so much for your help. I've checked a few things you mentioned and let me tell you the results.

The output selector creates no actions at all. I listened very carefully and it sounds as though absolutly nothing is happening when changing settings.

AC was working intermitantly until it eventually conked out completely. I'm pretty sure the AC system itself is OK. The AC light on the control does not come on. I jumpered the AC pressure switch ( small round 2 wire plug on rear of AC compressor, correct?) and it changed nothing. AC compressor still did not engage with pressure switch jumpered and AC selected at the control.

Gave it a try. The only controls that make a difference are the fan speed and heater control. I can hear an actuator moving with the heat control. Fan speed works normally. Outside air/recirc does nothing, AC button does nothing, vent selector does nothing. Lights on the AC button and recirc button never come on.

Disconnected the battery. When I turned on the fan again I thought I heard and actuator move but the same symptoms persisted. Tried a couple more times with no result.

Also, when I first installed the new controller, the lights on the AC and recirc buttons were on. Also, I think, the air did change to the dash air instead of floor level. The AC never came on though. After a minute I noticed it was venting from the floor and no lights.

Do you know if there are any other control modules between the dash control and the actuators that might be suspect? Also I am wondering if possibly one of the vent motors is stalled, blowing a fuse, fusible link, or the control itself? I would also suspect the new control could be bad, but the current symptoms are exactly the same as they were with the old control.

I'm wondering if there is an online source with a diagram of the location of all these HVAC dash components. Happen to know? Any other ideas?

Tremendous thanks for your help, Brian.

My '97 1500 has a fuse/relay box under the hood, next to the fender on the driver side.If yours has one, there may be a fuse/relay for A/C there.

Hi!

It doesn't sound good for the control. As far as I'm aware, the controller itself supplies power to the components that it operates. The only notable exceptions might be the A/C and fan, which seem to be controlled with a set of relays in the ones I've worked on.

Can you see any connections to ground from the control body or its wiring? Are they good and tight?

Still, you might look at the fuses and make sure they're really all good. Pull relevant fuses and check them with an ohmmeter. I've seen fuses that could look good but fail when loaded.

Sounds like a system potentially low on refrigerant charge to me. I'd defintely rule that out first.

I'm not aware of any, but then again, I've not worked on a '95 truck nor have I had the benefit of service literature to tell you.

Of all three possibilities, only blowing the control itself is a likely outcome. Still, I'd have to think it was reasonably well protected against that sort of thing. Actuator failures seem to be pretty common, but I've never heard of any that killed the control as well.

I don't know of any. What I would highly recommend is obtaining the factory service manual for your truck. You will be glad you did! I didn't realize just how true this was until I got the FSM for a Chrysler vehicle I was working on. Normally I'd found the Haynes and Chilton's books good enough, but both of the ones I had for the vehicle in question were nearly useless for the car I had. The Chrysler books were excellent.

Manuals for GM products are available from

Thanks again William. Did more poking around. I hotwired the AC compressor and immediately nice cold air came out, so I'm thinking the AC system is OK. Checked the fuses with an ohmmeter and they check out. Swapped in the old control and the system behaves identically. Reseated all the plugs I could get to in the dash with no changes. So, I'm at a loss.

At least I know that worst-case-scenario I could manually configure the selector and recirc flaps and jump power through the AC switch, low and high pressure sensors, and get the AC to work.... Thanks a lot for your help, Brian.

Hi!

Well...it really sounds more and more like two bad controls, or two controls that were damaged by the same thing. Can you take your controllers to another truck and see what happens there?

I'd definitely try manually operating all the actuators once you've got the pinout figured out (sorry I don't have one to offer you) and see if they work. If they do, then I'd definitely give thought to obtaining a known good controller. Install it with the battery disconnected and see if it works better.

William

On my '96 I've had two issues that had some of your symptoms. The first time it was a stuck relay which I "fixed" by tapping the relays under the hood on the left fender well with a screw driver handle. The second time I replaced the control head. And, I still have a bad actuator for the fresh air mix door. It would not stop at its open or closed limit and just kept clicking. It is such a PITA to change that I just "parked" it in a mid position and disconnected it.

Good luck, Mike

Mike, Did you get to open the fuse/relay box under the hood? On my '97, it's mountedon the side of the fender alongside the brake unit. It's hinged at the fron, but the lid only lifts about an inch before hitting the top of the fender. I was going to remove it to open it. After I removed the mounting bolt, it didn't look like there was enough wire to move it, and the brake unit is in the way.

Look at that box again. It's not hinged, it has the same kind of clips holding it on both sides. It should un-clip and lift right off.

Yeah, what JR said. That box is not hinged. It has the same clip on both sides and then the top just lifts off.

Yea, thanks for your suggestion William A. I checked out the fuses and relay and they look fine. I swapped the relay with another of the same type and no change.

Was just out trying to track down the problem and found that on the wires going to the AC compressor, I have continuity to ground on both of them, with the control unplugged. Doesn't sound right to me, but maybe thats how it reads with the pressure sensors in line? Anybody know?

Thanks again all, B.

Found an AC schematic, and it looks like the two leads are jumped together with a diode, so thats probably why its reading continuity to both. I'm starting to think I might have gotten a bad replacement control. Thx, Brian.

Figured it out! :-)

Yep, bad controls, both new and old. So how I eventually figured it out.... Was trying to get a grip on what parts of the system were working or not. So I hotwired the coil on the AC relay, click, compressor goes on. hmmm. Other two leads are for the relays coil, one was grounded, other wasn't. Checked for continuity between the ungrounded lead back to the AC controller harness, and found the lead that goes from controller to relay. cool. No power coming out of controller to power relay. Traced relay wire back through controller to AC pushbutton. no power. Hotwired power to "upstream" side of AC switch. BINGO! Everything worked normally.

So, I jumped power from the hot coming into the controller to the AC pushbutton and it all works. The board must have a bad connection or trace that I can't see and am now"backfeeding" the rest of the board.

So now I get to return the bad controller, keep my money, and have working AC :-)

Thanks for your help guys! Brian.

my 95 suburban is experiencing similar issues, however the AC button light comes on, i feel the relay 'click' when engaging the AC button but the clutch does not engage. fans and all work OK and fuses test OK

will low AC refrigerant cause the clutch to not be allowed to engage?

Correct, the low pressure switch will stay open keeping the compressor clutch from engaging. The compressor depends on the movement of refrigerant to carry oil to lube the cylinders and the valves of the compressor. The only compressor that didnt was the two cylinder air temp used by Chrysler.

Whitelightning

Ended up being a major leak in the evaporator...

Lots of leaves in the evaperator housing? Oak tree where vehicle parked?

Whitelightning

hummm...could have been. I didn't ask however its a possibility...