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Marty, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 54950
Experience:  Bosch Certified Master Technician with over 35 years experience in the automotive industry.
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When starting from cold and sometimes after car has stopped

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When starting from cold and sometimes after car has stopped for a short time, internal heater fan comes on full power on hot, it cannot be switched off by any controls and can stay on for upto 10/15 minutes then it will go off on its own. This is causing problems now the weather is getting warmer.
Car is E280, 2001 model tiptronic. with 109000 miles.
Can you help??.
Hi, my name isXXXXX this problem occur when the key is off?
Customer: replied 4 years ago.

No, problem only starts when engine is started. Approx. 30 seconds after engine is started fan comes on full power and will stay on sometimes for upto 10/15 minutes getting hotter as the engine warms up. On occasions fan will come on whilst car is being driven after travelling several miles and blows hot air into the car. Again it will stay on for several minutes before switching off again. An intermittent fault somewhere.

Ok, will this happen if you are using the air conditioning? In other words will the problem suddenly override the current setting of the climate control?
Customer: replied 4 years ago.

Hi Marty,

The car has air con not climate control. As I said in my original mail, you can not stop the fan by pressing any control or even switching the air con off.

Switching the fan control to off or adjusting the temp controls makes no difference. Even with the temp controls set at cold the fan blows hot air at full power into the car when it decides to come on !!.

Hope this info helps and that you can put forward a solution.

Customer: replied 4 years ago.

Is this a problem you cannot solve ???.

Hi Tony, sorry for not replying yesterday I never saw your reply in my inbox.

Can you post the vehicles 17 digit chassis number for me.
Customer: replied 4 years ago.

Hi Marty,

Chassis No of my car.


Trust this helps.


Hi Tony, there are two possibilities for this symptom. Either the a/c control in the dash is intermittently shorting or the electronic blower regulator at the blower motor is shorting. To test for this problem the white/pink wire to the blower regulator needs to be disconnected while the problem is occurring. If the blower turns off then the problem is in the a/c control in the dash. If the blower continues to run with the white/pink wire disconnected then the blower regulator is the problem.

Let me know if you have any questions.


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Customer: replied 4 years ago.

Hi Marty,


Thanks for info, will have this checked out and if necessary come back.



You're quite welcome Tony.

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Customer: replied 4 years ago.

You were right, it was the fault of the resistor on the heater fan.

Replaced, now OK.

Thank you,


I'm glad everything worked out Tony.