87 560 SEL Monovalve issues
 

Hello,

I have had to replace many a monovalve in my 126 over the past 14 years. This fall was no exception as the rubber was torn on my existing one. Ordered a new aftermarket part. Once installed - no heat. I do get heat if I disconnect the power supply and set thermostat to coldest setting. When I do that it blows full heat. Went under the hood today to inspect the new monovalve and the rubber is still intact. Connected power supply and again no heat. I know there are a pile of posts on this but I have a feeling that this could be the result of a faulty crappy aftermarket monovalve?

The Dude.

Heard the insert was available again from MBZ and have also heard a BMW insert can be used. I'd search for an OE insert.

Good luck!!!

The valve will be open when power is removed; power closes the valve.
One side of the valve winding is always hot (+12V), and the controller grounds/ungrounds the valve to adjust heat. The fault is in the controller.

The MTC/Aftermarket cartridges are also well known for being junk. They close too easily and will stay shut even if the controller is not calling for heat. It is often suggested to transplant the rubber from the MTC aftermarket cartridge onto an OEM core.

If the controller is not calling for heat, the valve should stay shut!

Clearly not enough coffee in the system when typing my previous reply. My statement remains valid, the relation between open/closed and hot/cold was reversed.


The point is - the MTC cartridge is the most likely culprit, not the controller.

The aftermarket mono valves are junk. I went through the exact same thing last year. New mono valve repair kit from the dealer solved the problem.

Good luck!

As suggested above, transfer the rubber to your old core.