It’s a 2008 LT 4x4 4.2 liter v6
Rats! I was hoping it was an earlier model.
Technical Service Bulletin #02-01-39-005 - (Sep 23, 2002) seems to describe your situation almost exactly but it only applies to 2002 and very early 2003 models:
“Some customers may comment about no cold air from the heating, ventilation and air conditioning (HVAC) system during a drive cycle. This concern may occur at any time during the drive cycle and at any temperature setting. The HVAC system operation returns to normal after the vehicle has been keyed to off and restarted. This concern is intermittent and most likely to occur on hot days. This concern may be found on vehicles equipped with manual (CJ2) and automatic (CJ3) HVAC systems […] An HVAC control module software update was put into all production vehicles beginning in September 2002. Vehicles built in September 2002 and earlier may need this software update.”
There was a later TSB for 2005-2008 models (07-01-39-007A-No cold air from vents, A/C inoperative, blows warm air (Sep 26, 2007)) but this was cancelled by TSB 07-01-39-007B (Dec 9, 2008). The original solution for this one was to reset the HVAC Control Module by removing and re-installing the HVAC control module fuse (in rear fuse block under driver’s side rear seat). The TSB cancellation notice said if problem occurs, diagnose using information in SI (GM Service Information, aka the service manual).
There was also a service bulletin for the cooling fan clutch and the corresponding PCM reprogramming that @TwinTurbo mentioned, but again this was pre-2008. This clutch should still be checked though.
The fact that power cycling fixes the problem, even if only temporarily, still suggests to me that it is a software or control issue rather than something on the refrigeration side, though all avenues of diagnosis should be followed. You could try doing the module reset for the heck of it, or maybe have the HVAC Control Module reflashed in case the software glitched somehow.
Wow! That’s crazy, I had no idea about those things but I will certainly try them!
Those are my symptoms to a T and yes it does seem to act up on the hotter days,that’s so funny. Where exactly is that fuse located under the driver seat? And how should I go about doing it?
Never mind I see it says under the rear driver side seat.
So I’m going to start today by resetting the hvac module under the seat and drive it on errands and see what it does, I’ll keep you guys posted on progress and if and when or what it is when it’s fixed!
Under the circumstances I usually just move on but I’m curious why you wouldn’t at least try checking the clutch fan as I suggested? Or even answer the first question…
Ok so I pulled the fuse and it did reset,however it did not fix the issue. Now for the stupid part… I bought a control module off eBay a little while back and forgot about it even with all this module talk lol,it’s in good shape and from a trusted parts dealer so I know it functions. I’m such an idiot I was sitting here looking up module recalibration on YouTube when it hit me I have one sitting in the garage. I mean it’s gotta be worth a try before I go having it hooked up to a computer again right?
I stated before about the clutch it’s been checked out and in fine working condition,sorry I didn’t mean to not answer you
Everything checks out under the hood,it’s something electrical
Just to clarify, the clutch to which @TwinTurbo is referring is the cooling fan clutch, not the A/C compressor clutch. Was that one checked out and determined to be okay?
Yeah it was the A/C clutch, I will check out the fan clutch. Sorry I guess I missed that…
there is no wiring harness on the compressor. Isn’t it a completely mechanical thing? I happened to take one apart yesterday out of curiosity what the inside looks like. 5 pistons and a bunch of passages for the gasses/fluid to flow through and get compressed. The only electrical part are to the coil, sensors and condenser fan.
The compressor itself is mechanical. If the electro-mechanical clutch works and is energized, the compressor should be doing its job- assuming the system has sufficient refrigerant. Checking high and low side pressures should verify these.
If the clutch is still engaging the compressor when it starts blowing warm, humid air and the refrigerant charge is verified to be in spec, then it is one of two things; the condenser fan is not capable of removing the heat by itself (see recommendation to check fan clutch for PROPER operation not just that it is turning the fan and understanding if it only happens at a standstill/low speeds due to inefficient fan) or the HVAC controls are switching the mode and/or blend door positions away from the selected cooling position(s).
1 Like
Well I think my issue is resolved, I put the new hvac control module in this morning before driving it all day and it hasn’t skipped a beat! So I think it was in fact something to do with the circuit board or software.
I found this video late last night that led me to believe it possible… https://m.youtube.com/watch?v=2vWHWP6GghE
congratulations, great work.
