ThumperNC24

Hello,

I just got my car back from the tuner and I am having serious issues with my A/C at idle.

My tuner said the car is not sending an A/C on signal to the ECU to adjust the idle. I think the car is trying to save itself from stall and it just cycles the A/C on and off as the idle rises and falls.

What actually sends the A/C signal to the ECU? How can I check this with a multi meter or similar?

Car recently got an all new LS3 and a new A/C compressor so I'm wondering if a wire got pinched or something.

Thanks

C5 Diag

About a year and a half ago I was helping one of our members whose AC would cut off at either idle or in park…his issue was in the tune so I would have your tuner check his work…if you had a Tech 2 of any bidirectional scan tool you can check your “AC Request” data PID to help diagnose…this Data PID would tell you if the HVAC Module or PCM were bad…if the PCM sees the correct “inputs”…RPM, ECT, AC pressure sensor, and ambient temp sensor it will ground the AC clutch relay control driver in the PCM and the clutch relay will engage (relay 34)

ThumperNC24

Unfortunately I don't have a Tech2, I wonder if I should just take it to a standard shop to see if they can scan for this.

I brought this issue up with the tuner and he swore there was no A/C request signal. He programmed a higher idle for A/C on but the idle does not go up at all when the A/C is on - he said this wasn't happening because the ECU wasn't seeing that the A/C was on.

C5 Diag

The first thing is scan for any HVAC DTC’s !!…I was messing with my AC clutch relay and had it removed for testing and when I installed it my AC would not work until I cleared the HVAC code…you can have your shop if they have a bi directional scan tool to go into the HVAC module and look at the data….press the AC button and if the AC Request does not say YES you have to check the HVAC Module connections…if the connections are OK it may be a bad HVAC module…if the AC Request says YES they should look at the AC Relay Command status and if it says OFF they have to check the connections at the PCM…if connections are good it may be a bad PCM…since you put a different engine in this thing with your ‘03 PCM that may cause issues with the PCM calibration…I kinda stay away from this kind of a diagnosis since I don’t know what I’m dealing with !!…if you need someone to look at the car I can recommend one of the top diagnosticians and automotive instructors in the country …his name is John Thornton and contact info below !!…he is not a standard shop !!…his company is in the Chicago area. !!…I attended one of his online misfire diagnostic classes last year during COVID and he sure knows his stuff !!

grinder11

I'm the guy C5Diag is referring to. My issue is still there, only because I haven't gone to the tuner and had him fix it. I have a modded engine with a fairly decent cam. I believe the tuner did this to obtain a better idle while vehicle is stopped in "drive" (an A4) with the A/C on. If your A/C works fine while moving, but stops when you are at a stop, this could be the problem. C5Diag is the guy to talk to about electrical stuff, he or Bill Curlee, GCG, etc. Could also be your condenser is full of crap like bugs, etc. Mine was. If that's the case, you could make an extension for your air nozzle, CAREFULLY put it down between the radiator and condenser, and blow towards the front of the vehicle. You'll be amazed at the amount of junk that comes out that's blocking airflow.......

bookyoh

First question is - when was the a/c last performing normally? Was it running without the compressor cycling after the new compressor was installed? If so, when did it stop running normally?

grinder11

OP may also want to post this in the scan/tune section. That's what I did, and that's how I was able to determine what the problem was. I know that, somewhere in the tuning software there's a way to disengage the compressor while idling at a stop.