Mono valve part 1984 300d turbo w123
 

I've searched the entire site and have not found the "mono valve".
I have bought an after market part made in China and it failed to function.
I heard that the genuine Bosch mono valve is no longer available.
Can you suggest where I can find this part?

By "mono valve" are you referring to the vacuum operated on/off coolant flow control valve to the heater core that's located underneath the HVAC air inlet screen below the base of the windshield on the passenger side?

Duke

On an '84, I believe the monovalve is electronically activated (my '85 is). One option is to find one in the junkyard, even if the diaphragm is torn. You can use the diaphragm from the rebuild kit you bought on the junkyard one. I haven't found markings on any of the (several) that I have sourced, but I believe that the aftermarket part has a higher polished solenoid housing, while the original Bosch ones are more of a matte finish. You might grab several if there are multiple donors at the junkyard, I've had to swap between a couple different ones until I found one that (seems to) work well.

Another option is to contact George Murphy from this forum, he may have some rebuilt units available.

The monovalve repair kits are iffy because quite often the electromagnet in the monovalve is defective which the repair kit does not address.