sixpack

The heater on my C250 Diesel does strange things. This model does not have aircon, just the basic heater. I have the temp. controls set to full cold. When you start the car from cold, it blows outside cool air to the vents as expected, but when the car is warmed up, then stopped for say, 5mins, then restarted, it blows very hot air for the next 5mins, gradually cooling back to outside temp air. Very uncomfortable as Scotland is having a very hot spell! Ive looked at the little fan beside the interior light, it spins ok. This model has separate temp controls for either side of the car & 2 water valves feeding separate sections of the matrix. I thought of disconnecting the plug from the water valve as temporary cure, but would this show an error code? Any other Ideas Anybody ?.

sph17

Greetings! Here in the US our w202 have A/C controlled by a Climate Contol System. Having owned three W123 I have experienced the same thing when the diaphram in the monovalve would tear. I don't know if your vehicle has a monovalve or if the "two water valves" are your equivalent of our monovalve. In a pinch I have used vice-grips or hemostats (medical item that is like a pair of blunt locking vicegrips) to clamp off the hot water feed tube. You might want to inspect your water valves more carefully.

Our monovalves are secured by four screws, and when the electo-magnet and valve are removed from the housing, the silicone diaphram can be inspected for tears, which are usually there and are the cause of the problem. Back in the 80's I could purchase a replacement diaphram for a few dollars, then MB decided to only supply the whole assembly for about $35.

Don't know if this helps or not.

Good Luck.

scorchie

I think all the W202 have duovalve ... (instead of monovalve). Not completely sure about this, but I know my 1999 model does have a duovalve.

Other than that, you're right about the having to replace the whole thing now!

-s-

sph17

scorchie, you are of course correct, as my 97 W202 has a "duovalve" also.

As this item has not gone bad on me (knock on wood) with my W202s I do not have experience with it. The monovalve though on my W123s has gone bad numerous times. I have a collection of old, broken diaphrams, and the electomagnets I had to buy just to get a stupid $1 silicone diaphram.

sixpack

Thanks for the replies,sph17 & Scorchie. I looked more closely at what the heater does when it goes hot, & noticed that both sides of the car blow hot air. This could only happen if both valve diaphrams ruptured at the same time. I hav,nt tried disconnecting the electrics from the valves yet, but that seems the next logical step.


Peter