560 Wacky heating system.

[embe560sl]

Help please.....what has gone awry with my heating system? it will not shut down or blow cool on the temp wheel and has to have button '0' pushed in (to stop all air flow) to be comfortable? air cond also not operating? are they inter related ? Any suggestions greatly appreciated

[Strife]

There can be a lot of causes, but one of the first and cheapest places to look is the monovalve, on the RH of the engine compartment behind and above the valve cover. It's a solenoid that opens and closes a valve bia a piece of rubber. If the diaphragm leaks in it you will be hot all of the time no matter what you do. The assembly is expensive but the repair kit, which fixes the problem the vast majority of the time, isn't. Note that I installed this repair kit twice, because I didn't install it properly the first time (duh).

[embe560sl]

Yes Strife, I found the unit....just remove 4 screws on top, plus electrical connection and you are there, right? is removing the valve any problem? finally and more importantly, what's the correct way of reinstalling the kit? you mentioned you screwed up twice.

[Alkraut]

I recently rebuilt the monovalve on my 560SL and it solved the problem of no heat for me. May work for you as well. Procedure is straightforward:

Use two pair of vicegrips or other locking pliars to pinch and close the two heater pipes that go to the valve.It's not absolutely necessary, but avoids some coolant mess. The valve is high enough so you don't need to drain coolant from the radiator.

With ignition key off, carefully remove the electrical connector on top of the valve, it has two snap legs. Remove the four slotted screws on top. pay attention to the orientation of the cover.

Remove the cover, the inside parts will come out.Hold the inner sleeve so it does not drop off. Note the position of the large and small steel washers and the wave spring. Make a sketch.

The replaceable part of the valve comes out with the tube that stcks through the cover. It has a couple of molded rubber parts and a mesh screen.It is all one assembly. The stem of this part moves in and out. Push the "cigar tube' part through the coil to remove.

The repair kit has a new one of these assemblies and usually a new wave spring. If the outer heavy metal sleeve comes off the large coil, reassemble with the slots toward the cover. I believe it fits in a position. Slide the new valve into the coil with the washers in the proper position. Insert the whole thing back in the housing, in the same way it came off.

Assemble and tighten the screws, it will pull the cover in place. Put connector back on and remove the vicegrips (if you used them). Good luck.

[embe560sl]

.....it sounds a little trickier than I had imagined....but with your terrific comprehensive description on 'how to'.......it will make the repair much easier. I hope I will have no difficulty in obtaining the 'repair kit'....we shall see. Thanks again, your knowledge sharing is very much appreciated.