'99 Tahoe - No power to compressor clutch?

[elsporko321]

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!

 

[SunlitComet]

If you have bypassed the low pressure switch and it worked and you can verify you have a good charge then most likely the switch is at fault. is that a scenario you have come across yet with just that switch bypassed and the rest of system intact.

 

[elsporko321]

Thanks! I've read quite a bit on here on various fixes for my tahoe as they come up - more problems than I care to admit - but I have a love/hate relationship with it.

The problem is that I bypassed all switches, including the A/C switch on the control panel. Whats confusing me is how to single out the low pressure switch when I can't confirm that the control panel is working. I guess I need to "jump" the A/C switch, but don't know what wires to isolate/jump and in which of the three plugs they are in.

The compressor clutch switch (plug on front of compressor) is not getting power. Its reading 0.08 volts, which is probably 0 as far as the compressor is concerned.

I tested the relay, and made sure the sockets are getting battery voltage (they are). I put a jumper on the low pressure switch and high pressure switch simultaneously and still got effectively 0 volts on the clutch switch.

Now one of two things is happening:

1) The control panel has a bad switch on it. This is the third one i've put in this car, and while possible its hard to believe that this one is also bad.

2) There is a short/disconnect in the power wires running from the control unit to the clutch switch. This seems much more likely, but also near impossible to track down.

It seems like the next step is testing the control unit and the wire from the unit to the switches. Do you know which set of wires control the compressor clutch?

 

[SunlitComet]

The controller if working properly would output 12volts on the dark green wire THAT DOES NOT go to to the fan switch when a/c is selected. start with that. And just in case you did not know the pcm is the middle man in this grand scheme of things. Keep that in mind as we move forward.

 

[elsporko321]

The controller if working properly would output 12volts on the dark green wire THAT DOES NOT go to to the fan switch when a/c is selected. start with that. And just in case you did not know the pcm is the middle man in this grand scheme of things. Keep that in mind as we move forward.

Where would I measure that 12v? The copper contact where the green wire would connect if it were plugged in? Sorry for my ignorance...decent with electronics (guitar amps, effects pedals, etc.)...not much of a mechanic, though.

 

[SunlitComet]

Should be number 10 Which I think is at the bottom and should be light green not dark green sorry.


Heater and A/C Control Switch

Notes

C3: Heater And A/C Control Switch

 

[elsporko321]

Thanks for the pic! I'll have to wait til tomorrow evening when the weather is slightly less terrible to test it, but will follow up after I do.

If you (or anyone else) can think of anything else to try, let me know!