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Hi all,
since the weather turned warmer i have an interesting situation with my car. I always keep my aircon on full auto, around 19-22 degrees celsius ( 60-70F) all year around, on all 3 zones. At nights, when the temperature is around 14-17C (57-62F) it starts pumping very warm air. Even if i go as low as 16C (60F) it still blows warm, only when i set it on LO it starts pumping cold air as normal. When it’s hot outside and inside (black paint on black interior) it works normally, only at night when the temperatures are as mentioned it makes this. For eg. if i start with the car hot and continue like that it pumps normal air , only when starting at 14-17 it pums warm air. Sometimes if i keep it longer on LO then set it back to normal temperature it goes back to normal, but not always. I have already cleaned the interior grille where the temperature sensor/fan is, behind the steering wheel to no effect. I’ve read that holding auto+rest might reset the system but to me it had no effect… Has anyone had similar issues? If yes, how was it solved? What should i try further?
* Aircon was checked in May last year and it had no leaks, refreshed the freon and lube (or oil ehatever its called)
Thanks all!
Hi all,
since the weather turned warmer i have an interesting situation with my car. I always keep my aircon on full auto, around 19-22 degrees celsius ( 60-70F) all year around, on all 3 zones. At nights, when the temperature is around 14-17C (57-62F) it starts pumping very warm air. Even if i go as low as 16C (60F) it still blows warm, only when i set it on LO it starts pumping cold air as normal. When it’s hot outside and inside (black paint on black interior) it works normally, only at night when the temperatures are as mentioned it makes this. For eg. if i start with the car hot and continue like that it pumps normal air , only when starting at 14-17 it pums warm air. Sometimes if i keep it longer on LO then set it back to normal temperature it goes back to normal, but not always. I have already cleaned the interior grille where the temperature sensor/fan is, behind the steering wheel to no effect. I’ve read that holding auto+rest might reset the system but to me it had no effect… Has anyone had similar issues? If yes, how was it solved? What should i try further?
* Aircon was checked in May last year and it had no leaks, refreshed the freon and lube (or oil ehatever its called)
Thanks all!
prepare your wallet for a mild sticker shock.
You have a lazy cooling without leak.
> If you DIY...
good chance you need a spare prop. valve.
> If you don't DIY...
this repair is a new compressor unit.
> If you like hard data...
troubleshoot AAC using your fav Mb scanner.
Look at sensors as compressor hardly able to pump down low side into your high side.
Keep as much heat you can out of high pressure line after condenser. ie. wrap your lineset heat exchanger.
welcome to JP van (not MB Vito)
Last edited by CaliBenzDriver; May 19, 2026 at 08:12 PM.
Are you using phone holder nearby the center vents by any chance? Mine used to do this (I had to go to LO to get cool air out). It turns out the phone holder was redirecting air from the vent to the temperature sensors nearby, hence sensor detected cooler ambient temp thus reduced the cooling output.
prepare your wallet for a mild sticker shock.
You have a lazy cooling without leak.
> If you DIY...
good chance you need a spare prop. valve.
> If you don't DIY...
this repair is a new compressor unit.
> If you like hard data...
troubleshoot AAC using your fav Mb scanner.
Look at sensors as compressor hardly able to pump down low side into your high side.
Keep as much heat you can out of high pressure line after condenser. ie. wrap your lineset heat exchanger.
welcome to JP van (not MB Vito)
Interesting take, i don't think the system/compressor is that lazy/faulty, when the car is hot it pumps cold air fairly quickly and consistent. Never had an error on the aircon system. i tend to think it is a sensor issue.. how could i check it?
Thanks in advance
Interesting take, i don't think the system/compressor is that lazy/faulty, when the car is hot it pumps cold air fairly quickly and consistent. Never had an error on the aircon system. i tend to think it is a sensor issue.. how could i check it?
Thanks in advance
You prefer data... this is option C: troubleshoot AAC using your favorite Mb scanner.
Look at sensors to see compressor able to pump down low side or not.... line Pressure, Temperatures.
Last edited by CaliBenzDriver; May 20, 2026 at 03:43 AM.
Use a decent scanner and check all temperature sensor readings on the car, see which one is OFF/BAD/DRIFTED
Start with ambient temperature and slowly see its decrease/cooler and use heater to make it warm too, see how the sensors response.
N70b1 Interior Temp Sensor with int.fan, is known to sometimes go bad or whacky data.
Use a decent scanner and check all temperature sensor readings on the car, see which one is OFF/BAD/DRIFTED
Start with ambient temperature and slowly see its decrease/cooler and use heater to make it warm too, see how the sensors response.
N70b1 Interior Temp Sensor with int.fan, is known to sometimes go bad or whacky data.
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)) I think i'll go to the mechanic again 
