BMW 1-Series Forum (F20) 135i - 1Addicts.com > Second Generation 1 Series Forum > 2012 BMW 1-Series Sporthatch (F20) Discussion > Air temp in cabin varies
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      12-16-2015, 01:50 PM   #1
Kannu
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Air temp in cabin varies

My mates car (f20 120d) every now and then blows really hot air into the cabin. Usually when cruising the temp is set to about 20 degrees and everything is ok, but sometimes it has to be set even as low as 17 degrees (this is during wintertime).

Any ideas what could cause such a high variation in air temperature?
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      12-16-2015, 11:55 PM   #2
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There could be several reasons
Less refrigerant gas in the system.
Temperature probe is either obstructed from receiving the ambient air temperature
Temperature probe is faulty.
It would pay to have it checked by the dealer if the car is still under warrantee.
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      12-17-2015, 03:54 AM   #3
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Quote:
Originally Posted by Kannu View Post
My mates car (f20 120d) every now and then blows really hot air into the cabin.
Oh yes, this is what I experienced in a (new, less than a year old, 4000+ kilometres behind) 3 Series loaner equipped with the currently basic "semi-" (single zone) climate system: it did spit portions of warm air occasionally unless set to "coldest". I disliked that quite a lot. My previous non-BMW's auto climate was smooth. I thought the under-auto-climate was just rough, designed to promote the full-featured dual-zone one which is hopefully smooth (I have a manually controlled ventilation so I can't be sure). It would be interesting to know it could be just a repairable failure, not a common feature!
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      12-17-2015, 05:29 AM   #4
RiczPT
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Check the position in the regulation of the knob in the middle vents, because I think that this regulates the temperature that blows from these vents, rather than the actual AC controller.

http://www.insideperformance.de/medi...23_720x600.jpg
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      12-17-2015, 05:35 AM   #5
Kannu
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Sadly the car hasn't got warranty anymore...

I phoned a local BMW-mechanic today, but he hadn't heard from such problems, so no luck there.

I browsed realoem and have couple of questions though:

1) There is only 1 cabin temperature sensor and it is located in the control panel itself? (part 64119287341)
2) The system also has a part called temperature sensor (64119238085) and a control unit (64119311850).

If it is a "sensor" related problem, it should be one of those three, right?

The first one is an easy swap, but where are the rest located? Deep inside the dash probably?
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      12-17-2015, 12:02 PM   #6
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Some new info...

1) It doesn't appear to make difference whether the ac is in auto or manual mode. This would suggest that the problem isn't in the temperature sensor?

2) After being parked for 45mins today, the upper wents blew hot air regardless of the regulation switch position.
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      12-17-2015, 02:21 PM   #7
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Quote:
Originally Posted by Kannu View Post
Some new info...

2) After being parked for 45mins today, the upper wents blew hot air regardless of the regulation switch position.
I've always found a degree of heat soak from the engine gets into the system when parked, so often get a initial hot blast, so it could be unrelated to the cruising issue.
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      12-18-2015, 03:58 AM   #8
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Sounds like the controller which sends hot water through the heat exchanger is broken, and consequently instead of stopping the hot water from flowing, it's allowing it through, and then the air coming in is being heated. This happened on my friends Nissan 200sx.
Because of this, with AC on, it might make the temp marginally cooler but thats it.

I've no idea where the valve is to send hot water in to the heater matrix. On my previous cars it was clearly visible under the hood on the bulkhead. You might be able to check it if there are externally moving parts on it. Meaning, turn temp up to max and then down to min and see if anything moves, or if it gets stuck halfway etc.
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