1996 c250 heater not working

Hi,
First of all I'm new to mercedes benz forums. I have a 1996 blue c250 turbodiesel which up until recently has been fine.
The problem is that when I turn up the dials for hot air, there is only cold air still coming through. I have spoken to a mercedes benz dealer and they said (although I can't remember clearly) there is a mushroom shaped thing under the bonnet which has likely gone wrong. I have no idea what I'm looking for so maybe someone could point me in the right direction?
Also, probably completely unrelated but occasionally when I first turn on the blowers, they don't come on sometimes until I'm actually accelerating... it's like I bumpstart the fans into action by pushing air through the vents by acceleration. Could it be related to the other problem or is it another issue?
Regards, George

 

You have a duo valve under the bonnet that could have failed,, is it the same temp from both sides.

The carbon brushes on the fan are either stuck or worn out, and yes the incoming air can start it when like this, you can drop the fan and get new brushes on Ebay

 

Yep the temperature is the same from both sides, what is this duo valve and how can I recognise it?

Also, thanks for the information, I shall probably seek one off ebay as you say

 

Hi,
The duo valve looks like the pic in this e-bay auction.
http://www.ebay.co.uk/itm/Mercedes-...arts_Vehicles_CarParts_SM&hash=item231d89cdf3
It is fitted under the bonnet adjacent to the brake servo just in front of the windscreen on the drivers side.
If you unplug it the heater I think it should default to hot, if it is operating correctly.