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Not experienced it on this car, or read about it, but the electric 'clutch' for the A/C compressor, which is what engages the compressor to serpentine belt drive, can fail. Start with pulling/cleaning the connector to the A/C compressor; maybe a dab of dielectric grease too upon reconnect. The fact that it does work at startup would seem to indicate it may be a wiring or relay type issue, although it is a complex system. Don't forget to test both cooling fans; other than those low-hanging fruit items, you'll just need to study up on what else causes the A/C compressor to shut down.
Could this really be ECM related versus compressor/control valve related?
I changed the plug going into the compressor as it was brittle and broke.
But made no difference really.
Has anyone with similar issues gotten this fixed and confirmed it was indeed, ECM related?
reason being, I did have my ECM 1 repaired due to slight water ingress…
Last edited by outerunknown; 11-21-2023 at 06:36 PM.
In my case, it is most definitely the ECU that is switching off the compressor. I confirmed this early-on by monitoring the compressor shut-off code with VCDS while driving. Whenever I would sense a loss in cooling, the "Current Shut-Off Condition" measuring block would switch from 0 to 12 (screen shot below). "0" means the compressor is on, and "12" means it was shut off by the ECU/ECM. I got these values from Tis’ the HVAC Season. The only thing I can add is that I discovered the condition only occurs when the tranny is in drive, or reverse. When I switch to neutral or park, the code will immediately switch back to 0, and cooling will resume. This doesn't happen now since it is cooler weather, but was happening a lot during the peak of summer. It was really random, and so I got into the habit of putting it into neutral whenever I could (while driving) to keep the compressor on.
Oh yeah... one more thing. During all this I never got any fault codes from the HVAC system!
Last edited by The Great S8; 11-22-2023 at 05:04 AM.
As of today, the aircon is only blowing warm air. Both front and rear.
The temperature control makes no difference.
I tried putting it into Park and Neutral, did not make any difference.
The compressor does not seem to be coming on...but then why warm air? It should be ambient air?
When I turn the AC and Recirculate buttons off, the blower roars but there is no air coming out of any vent.
Earlier it used to cool intermittently, now none whatsoever. Gas is still adequate.
Last edited by outerunknown; 11-22-2023 at 05:48 PM.
The 'blend' doors inside the system are what actually responds to the control settings and determine whether you get warmed or cooled air, or simply the ambient airflow, etc. You mentioned the blower is running, but no air is coming out of any vent/register, which indicates you've got either a mechanical fault, or the upstream control units, etc. With VCDS and some other VAGCOM scan tools, you can do system tests on the HVAC to verify blend door functions are working. If you don't have VCDS already, now's the time you really want/need the access it provides to do internal testing and control module validations, etc.
That's actually why I bought VCDS (my 3rd VAGCOM scan tool purchase), since I had a lighting control module problem my OBD-11 couldn't touch...it suggested I buy a new lighting control module, lol. Fixed my problem with the VCDS scan tool, yup. Not saying that'll happen in your case, but the VCDS can do so much more than simply pull trouble codes and perform maintenance resets.
I would like to resurrect this thread and chime in that I have the EXACT same issue as the Great s8 on my 2015 Audi A5 2.0T (cpmb flex fuel)
Did you ever find out what is causing this?
I get shut off condition 12 after starting the car cold and driving for a few minutes on a real hot day. I stop at a stop light an a/c shuts off for 30 seconds, then turns on by itself again. It repeats this randomly sometimes. Otherwise, A/C is fantastic I get like 35F at the evaporator, no codes in climate control, no other underlying issues with the vehicle.
Hi thanks for the idea. I have had the Q7 since January of last year and the battery has held strong, so I never really thought about it being part of the problem. Actually the problem has been gone all winter, and just popped up again last week when we had some warm weather. It comes and go with the season! grr. Last week when it happened it was just like what I explained before... it starts getting stale,no heat, but the cool air starts blowing once I shift into Neutral or Park. I hope I can figure it out this summer - black paint warms up so nice and toasty!
[QUOTE=The Great S8;25906258]Hi thanks for the idea. I have had the Q7 since January of last year and the battery has held strong, so I never really thought about it being part of the problem. Actually the problem has been gone all winter, and just popped up again last week when we had some warm weather. It comes and go with the season! grr. Last week when it happened it was just like what I explained before... it starts getting stale,no heat, but the cool air starts blowing once I shift into Neutral or Park.
So here's the thing. When in 'Auto' mode, this car uses an array of sensors and runs the A/C compressor as it determines necessary to control the cabin humidity level, as well as for meeting your temperature requested, etc. If you go into the MMI, A/C settings and ensure that the 'auto-recirculation' function is turned on, that will give you the best cooling performance in warmer weather.
So far as your ECU calling for the compressor to shut down, that is feedback loop driven, which generally means you've either got a sensor problem or the refrigerant charge in the system is slightly high, which would show up in warmer/humid weather when the compressor is running almost constantly. Given that your VAGCOM reading indicated 36 F degrees from one internal A/C temp sensor...that's really quite cold and suggests it is likely slightly overfilled with refrigerant. When the A/C system's pressure gets too high, then the high pressure sensor should send a signal to ECU, and in-turn the compressor should shut down to prevent compressor/system damage, etc. The other side to consider is that there are multiple coolant temperature sensors/sending units, which are known to fail and send false data to the ECU, and so those seemingly unrelated sensors can also have a detrimental effect, etc.
If anyone has added refrigerant to the car trying to 'make it blow colder' pre-sale, or perhaps after you bought it, then that is a likely cause of the compressor shutting down under specific warmer temperature conditions only. I've used the auto-store A/C recharge kits on many of my older cars in the past, and I can attest to the fact that you need to be really careful not to overcharge any A/C system, and perhaps not surprisingly, the level of charge (how much to put in) is impacted by the ambient air temperature.
Here's a bit of research data:
2. Overcharged refrigerant
Just like with low refrigerant, the AC in Q7 will blow warm air only if the AC system is overcharged with refrigerant. An overcharged system not only affects cooling performance but can also damage the compressor and sometimes can cause a major leak.
Ambient temperature affect on refrigerant pressure
The refrigerant pressure is affected by the outside atmospheric temperature. So, even if you recharged your Q7 AC at the recommended pressure, the system could still over pressurize when the ambient temperatures get warmer.
Most modern vehicles use R-134a refrigerant, but newer vehicles are increasingly using R-1234yf as a more environmentally friendly replacement. The pressure values based on ambient temperatures differ depending on the type of the refrigerant. Check your vehicle’s owners manual or look under the hood to find the type of the refrigerant your vehicle uses.
Connect the pressure gauge to the low pressure (L) port in Q7. If the pressure is higher than the recommended pressure, let some refrigerant out preferably into a rag to avoid exposure.
11-20-2023, 03:49 PM
