Hi to you all...I'm new to this site and trying to find my way around!...I have just purchased a great 260e with only one previous owner and full history....I was wondering if anyone could help with a fault I have....The car has standard heating without air con fitted.....I can only get hot air no matter what any position the dials are set to....I have to keep the blower motor off or I roast!.....any advice on this problem would be great. Thank you.

 

Sounds like your solenoid valve is stuck open. Disconnect the electrical connection and see if you get voltage with the heat on and no voltage with the heat off. This may be reversed. I'm not sure about mercedes but I know my old BMW 5 series wired the solenoid so the power was applied to keep the heat off. They did this as a failsafe so the heat would be on if the system failed. If the voltage is present and not present as it should be then the valve is bad. I believe on the W124 the valve is located over by the battery. It has a heater hose on both sides.

 

Thank you for the info....I will talke a look today....I think the valve you mention is by the brake sevo as i can see a double type valve with wiring from it....

 

It might help if you bothered to fill in your profile.
The valve is called a duovalve. The rubber seals perish and there's no repair kit. You have to buy a new one.