AC pressure (disable) problem in Tahoe

[stagrlee]

I have a 2004 Z71 Tahoe 4x4 with rear AC and 225K miles.  It has all original AC equipment so this is its first failure. No codes, no cold air. HP Tuners shows “AC Pressure (Disable)” and I am able to override that and get the compressor turning and cold air as shown in the video so the compressor clutch circuit is fine.  You can watch the voltage pressure rise when the compressor engages in the video. I replaced two pressure sensors, one on the Receiver Drier (two wires) and one on the discharge line (three lines) and still no spinning compressor.  The All Data shows a third pressure switch on the back of the compressor but there isn’t one on my truck and no wiring harness for one so I don’t think All Data is correct.  Since HP Tuners is showing “AC Requested”, I figure my HVAC control box inside the truck is working.  Any ideas?  Is there a safety pressure switch internal to the compressor and wired to the AC compressor harness?  Which pins on the ECU should I test out for broken pressure sensor harness wires?  Thanks!

 

 

[richard wysong]

My guess is that the freon charge is low. What are the pressures with the a/c on max, windows open, compressor running?

[stagrlee]

I’ll check it on Monday.  I didn’t hook up my gauge mainly because the >1.0 volt on the pressure side and being short of time prior to going on a road trip.  I figured that pressure voltage would unlock the computer to engage the clutch, but I’m not sure how the ECU is programmed.

[stagrlee]

My Hi/Low refrigerant pressures are good.  Switched from using HP Tuners scanner to my old Autel and have a B0229 diagnostic code on the HVAC controller.  Pulled out the fresh air, recirculation flap actuator and it is locked up.  Getting this thing out was not fun.  Anyway, I guess the HVAC controller disallows the compressor clutch when it looses control of the fresh air flapper.  Why HP Tuners shows “AC Disable (Pressure)” is another mystery.  I wouldn’t have coded the HVAC controller that way but it is what it is.  Parts come in tomorrow.  Probably time to repaint the dashboard anyway…

[kickass audio]

it kind of makes sense with HP tuners calling it that way. You have 2 ways to tell the compressor not to be on, being wide open on the throttle (WOT) or having a fault that tells it to stay off even when you want to tell it to turn on.

 

Seems weird to disable the compressor with the actuator failing but I can say that some cars will cycle the clutch when you are in recirculate mode but will let the compressor run full time when you're pulling in outside air too.

[stagrlee]

So apparently I screwed up the AC configuration when I added electric fans to my truck.  Playing around with Hardware settings in this screen and these settings allow the compressor to turn on and the FAN #2 to turn on in my 2004 flex fuel Tahoe.  Why these are right (or are they??) I have no idea…. Hack hack hack.  The recirculation actuator was a separate issue.  Had to replace my dash controller and the actuator to get that fixed but it still didn’t get the clutch to turn on…

 

Edited August 20, 2024 by stagrlee