frejo

My thermotronic/climatronic starts blowing cold air after a while, even though it's cold both inside and outside the car. It starts with blowing warm air, as it should, but when the temp seems to be as it's supposed to it changes into blowing cold air. And the fan speed also increases after a while. I have to change the temp into "HI" to get warm air again, and then, after a while, I can begin to lower the temp to 25-24 (C). And, after a while, it just starts all over again.

I've tried to reset by using the defrost and recirc buttons, it clicked and flashed for maybe 10 secs, but no change.

What can be wrong? A sensor, a valve of some sort, or can it be a computer perhaps? I'm grateful for any input

Thanks
Fredrik

Glyn M Ruck

Is this in Auto mode only?

frejo

No, the cold air comes in both Manual and Auto. The fan speed can be controlled as usual in manual, so no problem there.

wippet

The system is quite complicated, look here if it can help....
http://pdfuri.com/download-1

Glyn M Ruck

The sniffer sensor in the overhead console might be playing up. The aircon controls temp by mixing hot & cold air & something is causing the controller servo to vary the flap position.

The fan speed should only change on it's own in AUTO mode.

frejo

I did the test that is activated by pressing down the AC-button for a while and it turned out that the car thinks I'm having around 30 deg. C inside and 50 outside (ambience temp). This would be fine if it actually was true but since I'm living in Sweden 17-18 inside and perhaps 7 outside is closer to the truth. This was during the evening so there was no sun. There is something happening here I believe...

Glyn M Ruck

Sounds like temp sniffer sensor in the ovehead console. Of course it may be the main controller.

frejo

Is this expensive? Difficult to change? Will a Mercedes tech be able to find out by hooking up the car to a computer?

Thanks for your answers
/frejo

Glyn M Ruck

Best to get it on to a Star. There is a sniffer sensor & fan in the overhead console. There is an evapourator temp sensor & an ambient air sensor & a refrigerant temp sensor & so on. There is the dash controller module & the blend flap controller etc. Tying down which is at fault here could be difficult. I have seen no sign of one common failure on this forum. Sensors vary in cost between $20 & $50. Other bits & pieces get expensive.

Just having insufficient refrigerant pressure can cause erratic behavior until it drops so low that the temp/pressure switch shuts down the whole system to protect the compressor. The most common cause of trouble is low refrigerant pressure but yours sounds more complex.

Good luck!

LILBENZ230

Thermotronic is the one found in ALL post-facelift cars, right? No digital anything but an auto mode and dual temp controls? If so, couldn't he try the press and hold front defrost and recirc buttons to sync things up first? Mine gets wacky sometimes and that seems to fix it, although these control modules are prone to issues from my experience and reading others on the board.

PS - one more post to 10,000 Glyn

Glyn M Ruck

Both Thermatic & Thermotronic were available in ROW in post facelift cars. Thermatic is the more simple unit without sun sensors etc.

10,000 post achieved on:

https://mbworld.org/forums/c-class-w...t-process.html

Only realised it after posting.

frejo

Connected the car to a STAR. Turned out the whole panel has to be replaced. Not so funny in a car that I've only owned for hardly a week... And they are impossible to find used so it has to be a new one.

Thanks
/frejo

Glyn M Ruck

Sorry to hear that. The little controller panel is usually pretty robust apart from knobs on pre facelift models which you can no longer buy & require to purchase a complete controller unit.