AC Compressor doesn't turn off

[nrramse]

Hello - this is my first post on this forum!

I have an 02 Tahoe with the Flex fuel 5.3 V8, and the AC compressor runs when I don't believe it should. Here's some details:

• The compressor runs when the fan is on, AC button is off, and defrost is off.
• The compressor will turn off if I turn the fan off.
• The compressor will turn off if I remove the AC fuse on the left side of the dash
• The compressor will turn off if I pull the relay under the hood. I tried putting the horn relay in its place but get the same results.

The AC works great when I want it to, but with the weather getting colder I'd like it to not fight my heater.

Thanks, Newell

 

[nrramse]

No thoughts about this?

I have a theory that, because I can turn off the AC when the left-side dash fuse is pulled, that something is wrong with the controls on the dash. I plan to remove them to see if there's anything visibly wrong.

 

[SLCHOE]

Well considering the schematic says that the control request signal is first supplied by the HVAC control head and then passes through the ECM which then uses other inputs to decide whether to actually ground the compressor clutch control circuit, it's a little more complicated than that. More than likely it is your control head as they did have issues those years but further electrical diagnostics are needed to be 100% sure.

Here is the schematic:

If you have a scan tool that can provide lave ECM data, there is a PID that would be useful to see also.

A/C REQUEST: Should show ON in the correct modes and OFF when the compressor should not be on.

A quick test would be to watch that PID throughout the modes. I have a hunch that it will always say ON (A/C is always requested). If you unplug the control head connectors from the back of it, and it still says "ON", most likely you have A/C request circuit shorted to power somewhere in the wiring. If it changes to "OFF" (A/C is not requested) that would point to a bad control head.

 

[nrramse]

I think I'm following you. By "HVAC control head", you mean the heater and A/C controls in the dash? Is that also the same as the "HVAC Control Module" in the diagram you posted (thanks for that, by the way).

 

[SLCHOE]

I think I'm following you. By "HVAC control head", you mean the heater and A/C controls in the dash? Is that also the same as the "HVAC Control Module" in the diagram you posted (thanks for that, by the way).

Yes and yes.

The control head is the same as the front HVAC control module which houses the control knobs/sliders and switches.

BTW, manual or Auto A/C?

 

[nrramse]

I think I have manual A/C. Here's a picture of the controls:

 

[afpj]

Here's a stupid question...on condition 1, you say defrost is off, but is it set to tecirc? Recirc will trigger ac.

 

[SLCHOE]

Here's a stupid question...on condition 1, you say defrost is off, but is it set to tecirc? Recirc will trigger ac.

It shouldn't. RECIRC is Recirculate meaning the recirculation mode door switches air intake from cabin air to outside air. Should have noothing to do with the compressor function.


Edit: And yes, those are manual controls.

 

[nrramse]

Actually, afpj may be on to something. If I shut off recirculation, the compressor does turn off. Is it supposed to work like that? If it does, it seems like the AC light would come on when recirculation is on - but it doesn't. I'll see if I can find mention of it in the drivers manual.

 

[afpj]

We have auto climate, although not dual zone. If in recirc or front defrost, ac is on but ac light doesn't turn on. It's automatic, so moisture doesnt accumulate & fog the windows. Didn't know if your manual setup does the same like slchoe noted, but it sounds like it does.