Mercedes C220cdi w203 heater problem solved

[Yuri84]

Hi all. I want to share my experiance how i fixed problem with my heater in the 05 reg w203 merc. Problem was with heater only blowing very cold or very hot air and auto climate control would not work too. Found problem by messing about with heater when drivers door was opened and it worked,but as soon as i shut the door,heater goes back to blowing hot or cold and no way of adjusting temperature. So i called merc specialists and they told me that problem is overhead light control module,that it needed to be replaced.
So i went ahead and got myself second hand unit of pre facelift w203,but it only cured one thing and i could adjust temperature,but climate control in auto wouldnt work. I found unit with same numbers as mine and now all works as it should.
Hope this might help somebody.
Best regards.
Yuri

 

[HITECH]

Thats a weird one. Ive got same car. Gotta replace one of the stepper motors clicking away behind the dash when start the car for for few minutes. Good to know when Im testing out everything. Cheers.

 

[Yuri84]

Thats a weird one. Ive got same car. Gotta replace one of the stepper motors clicking away behind the dash when start the car for for few minutes. Good to know when Im testing out everything. Cheers.

In my case,all motors,flaps etc are working...touch wood.
I contacted guys from merc club in Russia and they confermed that its know problem. That overhead unit has a temperature sensor built in and it was faulty apparently. Star diagnostic didnt show any faults though.

 

[yuriboy]

Hi yuri84,
I thought I was the only Yuri in the uk

 

[Yuri84]

Hi yuri84,
I thought I was the only Yuri in the uk

Hi. Yep,not very common name around here

 

[Yuri84]

Hi yuri84,
I thought I was the only Yuri in the uk

Do you buy chance own a star diagnostic? I am in Hereford and would like to do a full,proper check of all modules in our car.

 

[andy.alias]

Just ordered one off eBay in the hope it fixes the same problem for me. Bought one from a low mileage car that had all the cables attached as I can’t disconnect one of the wires on my current unit.

 

[Kerabo]

Andy.
this seems the only way I could contact you.
I found an old post about your w203 heater either Full Hot or Cold.
did you solve this?
I have the same. I done a flap reset and either that or something else started this.
thanks Ken

 

[Kerabo]

Hi all. I want to share my experiance how i fixed problem with my heater in the 05 reg w203 merc. Problem was with heater only blowing very cold or very hot air and auto climate control would not work too. Found problem by messing about with heater when drivers door was opened and it worked,but as soon as i shut the door,heater goes back to blowing hot or cold and no way of adjusting temperature. So i called merc specialists and they told me that problem is overhead light control module,that it needed to be replaced.
So i went ahead and got myself second hand unit of pre facelift w203,but it only cured one thing and i could adjust temperature,but climate control in auto wouldnt work. I found unit with same numbers as mine and now all works as it should.
Hope this might help somebody.
Best regards.
Yuri

 

[Kerabo]

Yuri
I have this heater problem. I know the top unit has a fan but didn’t know it had temp sensors. I was going to change the bottom control but maybe I should try this. Does it have to be programmed after fitting.
mine is 2006.
I done a flap reset and blew dust from the top and bottom and this started.

Thanks Ken

 

[Yuri84]

Hi mate. It does not need programming,but what i found is that it has to be same number as on your old one. Before buying one on ebay with same number as mine i found one unit locally,but that was from 2001 car which is pre facelift and that didnt work correctly,cant remember what exactly,but had to return it. I imagine that one from facelift model should be ok.
Its straight forward job.
Hope you will sort it out.

 

[Kerabo]

Thanks for that.
its More than just a fan up there by the look of it.

thanks again
ken

 

[Yuri84]

I am not sure there is fan there. Its that light overhead by rear view mirror. It has temperature sensor there.
You can test if its not working. Try starting the car and keep drivers door open and if temperature can be adjusted then it that light module. As soon as you shut door it then goes back to either hot or cold setting.

 

[Kerabo]

I am not sure there is fan there. Its that light overhead by rear view mirror. It has temperature sensor there.
You can test if its not working. Try starting the car and keep drivers door open and if temperature can be adjusted then it that light module. As soon as you shut door it then goes back to either hot or cold setting.

That’s great help.
thank you

 

[chrisk2010]

Glad you got it sorted it's an odd one but very interesting and good to know thanks for posting.

It reminds me of when the cruise control packed up on a previous Merc and it turned out to be the brake switch, i was ready to pull the steering wheel off and replace the multi function indicator switch but thank fully a quick trip to merc for the part and 20 min DIY fix sorted it.

 

[Yuri84]

Yep,it is odd one. I took it to merc specialists and they wanted to replace aux heater thats packed up and wanted 700 pounds for it and they were saying my air temps are not working because of that. Most garages just want to swap parts at our expense.
Hope it will help somebody else.

 

[Kerabo]

Yep,it is odd one. I took it to merc specialists and they wanted to replace aux heater thats packed up and wanted 700 pounds for it and they were saying my air temps are not working because of that. Most garages just want to swap parts at our expense.
Hope it will help somebody else.

Wow £700. I want a car for that.

Well I got it up to temp and if I open the door it makes no difference. Wonder why the door is in circuit?

Once the engine is hot and if it’s on climate control auto. On the lowest setting it’s full speed cold. Every setting above that is full speed hot. Until the engine is up to temp it’s more or less as it should be.

I already have the lower control and can get the top for £20. I don’t mind spending that but have a horrid feeling a flap is stuck.
I assumed when I blew the dust out it damaged something but I had a look inside of the lower control if very robust bad dont think that would hurt it.

you was lucky you found the answer on yours.

Thanks Ken

 

[Petrol Pete]

Maybe the door is in the circuit because with the doors open the car will be trying to heat/cool the entire world ? Bit like those hotels, if you open the window or remove the lock card from the wall slot the air con switches off .....except that they are easier to override than most problems on a Mercedes Benz .

 

[Kerabo]

Maybe the door is in the circuit because with the doors open the car will be trying to heat/cool the entire world ? Bit like those hotels, if you open the window or remove the lock card from the wall slot the air con switches off .....except that they are easier to override than most problems on a Mercedes Benz .

That crossed my mind but I thought No they wouldn’t do that.
I think your correct though.

 

[Petrol Pete]

Mercedes Benz sometime work in mysterious ways and have been known to do strange illogical things in their wisdom. But changing what the air con does if the doors are left open might be sensible. I have a 2006 C class I will try it one day.