New CLS fan speed has a mind of its own ???

[smillion]

I have a lovely new (2011) CLS 350cdi but am becoming more frustrated by the heater fan, and the apparent inability to control the fan speed and so get a quick demist/defrost on these cold mornings ....

On a cold morning you would like to think you could use the front screen demist funtion, however it simply is not powerful enough when the car is cold, especially with the car at idle. If I therefore select manual fan speed and put to "max" the fan simply refuses to increase speed unless the engine revs are increased. and so I can sit there on my drive at 3000 rpm to acheive a faster fan speed, but if i let the engine revs drop then the fan speed drops .... does anyone know why this is?

The same happens once you have set off; fan rises in speed in tune with the engine revs. Come to a juntion, stop, and the fan speeds drops away.

The dealership have suggested that is it part of the Blue efficiency system and that the car needs to come up to temperature; which is a bit odd when you need the fan speed straight away, at idle, and not after 10-15 minutes.

Does anyone else experience this in their Merc?

Thanks in advance

Marc

 

[rob_miller]

On a cold morning you would like to think you could use the front screen demist funtion, however it simply is not powerful enough when the car is cold, especially with the car at idle. If I therefore select manual fan speed and put to "max" the fan simply refuses to increase speed unless the engine revs are increased. and so I can sit there on my drive at 3000 rpm to acheive a faster fan speed, but if i let the engine revs drop then the fan speed drops .... does anyone know why this is?

Exactly the same issue on my 2011 C250 CGI. Low RPM gives me a lower fan speed whilst a higher rpm of 2000+ allows the fan to go up to max.

As you are experiencing the same issue I guess it must be normal.

 

[RichardM]

I had a play with mine Marc and at standstill on a cold start with the demist button pressed the fan is on speed 6. You can tell that by pressing the up or down button and see the next speed it goes to, then if I press demist again and it will go to 6.

I've not noticed the fan coming on that much more (if any) when I then drive off or if I was to rev the engine.

 

[saorbust]

Could it be your fan speed is kept low as the engine isn't warm yet ? You'd be overcooling it by dragging in the air.