Guess What? Another 1999 Tahoe AC problem here...

[N813]

I have searched up and down these forums looking for my particular problem and I can't find one.

I bought this awesome piece of nightmares back in March. Knowing that the heater and AC did not work. In the winter I worked on the heater. Figured out every blend door actuator was broken. I disconnected the wires and removed all actuators but the recirculating one (the hardest one), stuck a screw driver in the climate control mode door to keep it open so I'd have heat.

Now it's summer and naturally I want AC. So I start plucking away. Absolutely no freon in the system. Checked all fuses, was good there. Next I checked the compressor by jumping the relay, that worked. Today. I'm checking pressure switches.
Swapped out the AC relay for the Horn Relay. Started it up, hit the AC button on the dash, and turned the blower on full. Pull the wire off the condenser jumped it and nothing, pulled wires off of compressor and same. Grabbed my test light. No juice to either.
I do have juice to AC compressor relay switch though and to the ac fuses inside.
I noticed the little amber light inside the AC button either doesn't work or is not on.

So what am I missing? Need some fresh eyes. Do all the blend door actuators need to be plugged in to make all this work?
Or could it be something as simple as a bad AC button in the dash??...I'm probably not going to be that lucky huh? lol.
Where do I start fellas? Talk to me. Thanks' in advance.

I ordered new 'o' rings and gaskets, pag oil, clutch cycling switch, and new blend doors. I figured I better stop till hear otherwise.

 

[ScottyBoy]

I can't say for sure what's causing your problem, but I DO know something you need to be aware of. I can tell you both from experience of owning a 96 C1500 in the past, and my brother owning a 99 Suburban, plus I worked in a car audio shop, so I ran across this issue a LOT. The AC control board on the 95-99 trucks and SUVs has the actual circuit board completely exposed, it's not encased or covered or anything. So if anything metal touches that board while the ignition is on, that board is toast. But it won't just fry the board though. It will still work, but only in defrost mode, or the recirculate button won't work, or the AC button won't work, etc. So when I was installing radios in these trucks, I had to be EXTRA careful to cover all RCA cables with tape, and even blank RCA jacks on the back of the radio if they were the hanging pigtail style. I would also usually cover the circuit board with some duct tape to give it a little protection.
After the shop I was working at had to replace a few of those AC control units for customers, we all were VERY vigilant about taking all precautions to not fry anymore of them.
Also, if I remember correctly, you could replace the bulbs on those control panels. It was tiny bulb based on the rear of the housing that you turned a quarter turn with a small flat blade screwdriver to pop the bulb out. And I think the AC button and recirculate button each have their own bulb. So you can try swapping the bulbs around if you know one or more of them works. Move the good bulb to the AC button to illuminate it. If it still doesn't light up after swapping in a known good bulb, then something might be going on with that control panel.

So my best advice to you is to try and test your AC control panel in a friend or relative's truck if at all possible. If you KNOW the AC is working fine in their truck, then plug your panel in and see if it functions fine, or if ANY issues arise after installing YOUR control panel. That was the easiest way I knew how to diagnose a bad panel back then. But then again, 20-25 years ago these OBS trucks were EVERYWHERE, everybody knew someone who owned one.

 

[Hoesgottaeat2]

Good advice @ScottyBoy

 

[N813]

I can't say for sure what's causing your problem, but I DO know something you need to be aware of. I can tell you both from experience of owning a 96 C1500 in the past, and my brother owning a 99 Suburban, plus I worked in a car audio shop, so I ran across this issue a LOT. The AC control board on the 95-99 trucks and SUVs has the actual circuit board completely exposed, it's not encased or covered or anything. So if anything metal touches that board while the ignition is on, that board is toast. But it won't just fry the board though. It will still work, but only in defrost mode, or the recirculate button won't work, or the AC button won't work, etc. So when I was installing radios in these trucks, I had to be EXTRA careful to cover all RCA cables with tape, and even blank RCA jacks on the back of the radio if they were the hanging pigtail style. I would also usually cover the circuit board with some duct tape to give it a little protection.
After the shop I was working at had to replace a few of those AC control units for customers, we all were VERY vigilant about taking all precautions to not fry anymore of them.
Also, if I remember correctly, you could replace the bulbs on those control panels. It was tiny bulb based on the rear of the housing that you turned a quarter turn with a small flat blade screwdriver to pop the bulb out. And I think the AC button and recirculate button each have their own bulb. So you can try swapping the bulbs around if you know one or more of them works. Move the good bulb to the AC button to illuminate it. If it still doesn't light up after swapping in a known good bulb, then something might be going on with that control panel.

So my best advice to you is to try and test your AC control panel in a friend or relative's truck if at all possible. If you KNOW the AC is working fine in their truck, then plug your panel in and see if it functions fine, or if ANY issues arise after installing YOUR control panel. That was the easiest way I knew how to diagnose a bad panel back then. But then again, 20-25 years ago these OBS trucks were EVERYWHERE, everybody knew someone who owned one.

Well there has been some stereo work done by previous owner and myself more recently, but wouldn't that cause a blown fuse somewhere?
This thing has been a wiring nightmare, I've had to unf**k a lot of stuff. Guess it's time to take the dash apart and see what's going on back there with the control panel.
If I replace it, I'll definitely take your advice on covering it up and being extra cautious. Thank you
Well

 

[N813]

Okay, happy to see this! Control module circuit board has a burn on it. Looks like it's on the #5 wire which is brown and that's the only wire that has power to it. I read on another thread that the light green wire should have power with fan on and ac on and mine does not. I'm going to try and jump it tomorrow.

 

[east302]

Here are the wiring diagrams, maybe it will help if you run into other electrical gremlins…

 

[N813]

Here are the wiring diagrams, maybe it will help if you run into other electrical gremlins…

Much needed. Thank you sir

 

[YukonGTmaster]

I replaced all the large components in my '97 GT's A/C system, charged it up, took the filler hoses off, and the $20 ball/shrader valve barfed it out. Cheap insurance to change both of these low pressure & high pressure side valves when maintaining the system.

 

[ScottyBoy]

Well there has been some stereo work done by previous owner and myself more recently, but wouldn't that cause a blown fuse somewhere?
This thing has been a wiring nightmare, I've had to unf**k a lot of stuff. Guess it's time to take the dash apart and see what's going on back there with the control panel.
If I replace it, I'll definitely take your advice on covering it up and being extra cautious. Thank you
Well

Actually NO, it will NOT blow a fuse. It will ruin the control board if anything metal touches it, instead of blowing a fuse. At the car stereo shop I worked at, we discovered this and it happened so often that we kept a new control board in stock in case it happened to something we were working on.

 

[N813]

Actually NO, it will NOT blow a fuse. It will ruin the control board if anything metal touches it, instead of blowing a fuse. At the car stereo shop I worked at, we discovered this and it happened so often that we kept a new control board in stock in case it happened to something we were working on.

10-4 on that. I ordered up a new one. I'll be cautious when installing. Already made changes to stereo wiring to avoid anything dropping down. Thanks for that advice.

No updates. Procrastinating on taking the dash apart and getting everything ready for when the new recirculation actuator arrives. I'll look at the heater core and evaporator core see if they need replacing as well since I'll have everything apart. Talk about a can of worms. lol.
I'll feel better once the interior stuff is back together and working and then move on to all the HVAC stuff under the hood.