Headache Ball

Bought my GMCPO Impala LTZ in May, very very pleased, even slapped a couple photos up here somewhere. Anyway, not long after I noticed some gremlin type activity with the AC. With both switches all the way down, it should run recirculated air, and it does, most of the time. However, every now and then it will get stupid, and switch, all on its own, to fresh air, sit there anywhere from 4-16 seconds, then switch back to recirc. I drive 29 miles to work, and most mornings, no problem. Air at the vent is 48 degrees the whole trip. Going home though.... it will perform this little magic trick anywhere from 2 to 22 times in that 29 mile ride, and when it does, the air temp in the vent rises to 65 degrees. Now for the funny part-
First trip back to the dealer, you guessed it, could not duplicate the problem. No worries, I know it will do it again.
Second trip... yeah the system appears to be a quarter pound low on refrigerant. We recovered and recharged, everything should be good. Really? I say. Where did that 4 ounces of R134a go to? Anyway, that didn't fix it.
Third trip: It's back at the dealer, today marks one full week they have had it, and it is still playing games. I am claiming that the control module is faulty, shorting, or not fully plugged in. There has to be something either in the wiring harness or the control module that is screwing up. Oh no they say, It's most likely in the compressor.
Dudes, I'm pissed. I may need an AC refresher, but since when does the compressor control the module and not the other way around. This dealer has sold its last vehicle to me. Sad too. Sales side of the house has their act together, but service is about to have an obstinate, dysfunctional veteran all up in their guts.
Thoughts? Suggestions?

Headache Ball

UPDATE: I am told that GM has had some issues with the dessicant bag rupturing inside the receiver/drier and contaminating the condenser. Not sure I buy that explanation, not until I see the drier cut open and the dessicant dispersed. On top of that, regardless of a system flush, the compressor may already be damaged. I'm growing more suspect every day.

cleveland63b

is this happening in auto mode? Depending what the module sees it will cycle defrost mode to keep the windshield from fogging and recirc mode will not operate in defrost...just a thought


I personally am not understanding how a physical problem or leak in the AC system would effect the recirculation mode at all...but I may need to refresh on the newer systems again.

Headache Ball

Hey man, I'm with you. When I brought that up, they were very sure of themselves in thinking that there are two different problems. My issue with that is that when it cools-it cools well. I have my thermometer in the dash and it is pumping our 48 degrees. When it starts to act silly and switches from recirc to fresh, the air temp in the vent rises to as high as 65. How that translates to a physical problem in the system is also beyond my scope of expertise. How on earth does the compressor tell the module what to do? I don't think it does.
So here's my latest update: I got the call that all was repaired on Wednesday, so I went to pick it up. First gripe- they had my car a week and two days and put about 150 miles on it. That's not the gripe, my gripe is that it was running on fumes when I got in it. Just poor service, imo. Took it home, went to work the next morning, nearly froze to death in the car-just the way I like it. That ride home though.....in less than 10 minutes it was up to the old ways of dancing back and forth between fresh and recirc, with vent air at a balmy and humid 63 degrees. It goes back to the dealer for the fourth time for the very same problem this afternoon. Four trips to the dealer in four months of ownership.....you're better than that Chevrolet. Get your $*&T together!

BTW, cleve--my car doesn't have an auto mode. I keep it on max cool, and it should stay on recirculated air unless and until I physically adjust the temperature levers.

tech2

the previous gen trucks had to have the hvac module reprogrammed to correct the hvac system from going into recirc mode. the dealer should have checked for updates and tsb. updated programming may not be available.


not sure why its changing modes; if it works like the old systems, the module control the actuators that move the doors.


Sounds like they have been driving it to try to reproduce the concern...which is better than the first time and no fault found. Sometimes intermittent faults can be hard to find and fix.


Did the temp problem get fixed at least? I was wondering if the temp blend door was moving as well, causing the temp change. I would monitor all the door positions when the fault is active; to confirm un-commanded door movement.
Keep bringing it back.

Headache Ball

Everything works as it should...until it doesn't. I probably should have driven it with my own scan tool attached to it to see what all was going on. But to answer your question...no. I left work yesterday, about 40 miles to the dealer, and the temp at the vent never got below 55- that's with AC on max and a fan speed of 5.
Is there a way for me to post a video up here? I have the whole mystery switching episode on video.

tech2

a person could......if the temp blend door is easily accessible, set the temp to full cold and unplug the actuator then test drive.
if the system goes hot, the module and doors are ruled out

Headache Ball

Okay...I think I have figured out how to attach the video.Disclaimer- it's a phone video and attached sideways, sorry bout that. It won't win an oscar, but it will show you just how this thing is behaving. The problem I am having with my dealer's explanation is that I don't believe that the components of the system tell the controller what to do. The controller tells the components of the system what to do.

Nav613

GM had a lot of early problems with Temp blend door actuators, as mentioned above, one of these, under the dash, more than likely, "COULD" be your problem.
Happy Motoring

Headache Ball

Thanks NAV. Most recent update. I called the Buick/GMC dealer across the street from the Chevy dealer that has been tinkering with my rig. I cannot go back to that service department without bail money Anyway, they want to look at it, seem to think that there is something going on with the control module....Well duh. They will get one chance, and if they can't take care of it, I will take the car back to the Chevy dealer for a replacement or refund.