Hi there, I'm a new member so try to be patient. My Benz is not delivering heat at highway speed but will (for a few minutes) if I turn the engine off, wait a few minutes and then turn the engine back on. I also have consistent heat (at idle only, not highway) if I disconnect the mono-valve lead. I have replaced the thermostat and mono-valve diaphragm. The magnet appears to be working and so too the heater electronic control. I'm told the aux heat pump is only there to ensure good heat at idle and so don't understand my problem unless it could possibly be the check valve below the mono valve. Has anyone ever had a problem with the check valve ball? The car has only got 82,000 miles and the six cylinder runs strong.
Al

 

Hi mikal103451

Luckily I didn't have that problem yet, but a friend on our german forum had a similiar problem. As you have replaced the valve with an aftermarket one (as Bosch doesn't produce them anymore) the problem could be the little hole which you can see in his picture below is furher out on the aftermarket unit as the original (image). Maybe check that and make the hole a little bigger so that water can run through.


( image taken from http://www.w126-forum.de/read.php?1,...396#msg-363396 )

I haven't opened one yet, but as I understood, the sieve insert of the aftermarket valve sits to far over the little hole and close it up.

Greetings

 

I have since my last posting destroyed (drilled out) the check valve ball, then reinstalled the unit and found no difference, (no heat at speed, idle only). I then removed the unit and checked the magnet further and found an issue. I found that the magnet did not close or seat the diaphragm completely, it moved it only half way down to its seated position. I worked on it (loosened it) for a little while on the bench and found it (the magnet) would hold the diaphragm closed only for a while, but then it allows it to open again. In the absence of any other info I'm going to assume the mechanical part of the magnet is incapable of holding the diaphragm closed perhaps as a result of a weak magnet coil.

 

Did you replace the vacuum-motors (actuators) that run things to do with the heater?
I think there are 4 or 5 of them, and they're not too expensive from German Auto Supply LTD- a Ebay Store.