'99 Tahoe - No power to compressor clutch?
 

Hey everyone,

I've been without A/C in my Tahoe for a while now, but I just can't bear it any longer in this crazy Texas heat.

The A/C will blow, but the air is not cold. I know the blend door actuator is good, but need to replace the position actuator (currently removed it - have it permanently blowing to dash at the moment).

When I check the clutch plug for power, it doesn't have any. I have read that the low pressure and high pressure switches are in series between the control panel and the compressor; I've put a jumper on the low pressure switch, but no luck. I checked the 10A fuse and its good. I know there is a relay involved in the cluster under the hood - is there a way to test this part of the circuit with a multimeter?

For a short time I bypassed all switches and confirmed that the compressor runs fine independently of the control panel and switches (may need charged, but does run and cool). What would be the best next step to tracking down the culprit?

I have two AC/Heater control panels and tried both; they work fine, other than the fact that the backlights for the A/C and recirculate buttons don't work. When the light sockets are pulled, the air blows audibly louder. Tomorrow i'm going to get some #74 bulbs to replace them (Toshiba v-2 sockets).

The reason I even have two of the control panels is that the ground wire in one of the harnesses was not heavy-duty enough (a well documented issue) and melted through the plug to the point it lost connection, which caused the otherwise perfectly good panel to fail. I didn't find this out until I had the new panel in my hands and thoroughly inspected the old one.

The only thing I can think of is that a wire somewhere between the control panel and switches is shorting, or possibly very close to the panel itself. I'm guessing the best way to eliminate the control panel is to put a jumper between the A/C switch, but there are three plugs on the back of the panel, and it seems that each has the same green/black wires that I see going to the pressure switch and clutch switch so i'm not sure which two wires to jump.

Thank you all for your help!

Check you relay in the under hood panel. There are a few relays in there that are the same - I believe it is a 4 prong. Just swap it with on of the others like the horn or brake lamp relay (one that you know is working).

Checked the relay sockets to make sure they are getting power and they checked out good. I checked the relays for continuity, and they were also good. I swapped the brake light relay (know it works - i have brake lights) and still no go. I also double checked the fuse again just so it didn't get overlooked, and it is still good.

I put a jumper on the low AND high pressure switch, eliminating both, and still measure 0 volts to the clutch switch. The way it looks is either the control panel is bad (this would be the 3rd one I put it, so unlikely but possible), or the connection between the control panel and the clutch switch is bad (much more likely).

I'm up for any suggestions on how to go from here, or the best method to track down a cut/short in the wire. Which plug/wires am I tracking down, as far as which send power from the control unit to the rest of the system? As I mentioned above, I see that the switches have green/black wires, but there are multiple green/black from the control panel. If I know which ones control the compressor clutch I can jump those and isolate the control panel from the wire from the panel to the switch.

Thanks again

The wiring schematic in a Haynes might help chase the wires but even better would be to see if a local service center will print you a copy off of All-Data. That printout is usually in color, more specific and easier to follow. Do you have proper voltage to the switch ? If so, you could stretch a jumper to the clutch. At least that might isolate the switch and help avoid chasing through the harness.

Where would I measure the controller switch to know that its getting power? I know its going to be where one of the green wires connects, just not sure which one (there's 3-5 green ones connected to the back in various plugs, can't remember exactly how many).

In other news, its still hot enough at 9:30 pm to cause a Micheal Jordan sweat.

Ahhhhh, without a schematic in front of me, I couldn't tell you to be honest.

someone linked me a pic, looks like its the 10th connection (light green) on the long connector.

Did you check fuses under the hood and on the side of the dash?

Yes, the fuses on the side of the dash, and the fuse/relay under the hood all checked out.

I would lean towards the control panel then. I just did one and when the relay is bad there is still power to the cycling switch, but no power to the compressor. Mine was a bad relay. Do you have power to the cycling switch?