Monovalve question - PeachParts Mercedes-Benz Forum

Ether · #1 08-21-2007, 03:14 PM

This question pertains to a 1984 300D.

If I pull the electrical connector off of the monovalve what position would it rest in? Open or closed?

LUVMBDiesels · #2 08-21-2007, 03:22 PM

Open. To close it you need to put 12v across the connectors

Ether · #3 08-21-2007, 03:23 PM

Ok. Thanks.

I assume that open means coolant flow to the heater core?

LUVMBDiesels · #4 08-21-2007, 03:33 PM

Yes.. open = water flow to the heater. It is the default setting for the valve.
If you are having trouble getting 12 volts, check the connector itself. Mine had a loose wire that I needed to solder back on.

FRANKNBENZ · #5 08-21-2007, 05:30 PM

I'd also do the pins and the pin receptacles with some spray electrical contact cleaner. That stuff is magic on questionable switches too. Just keep it off the painted icons.

Good luck.

Ether · #6 08-23-2007, 09:34 PM

I discovered that my original issue with the monovalve was due to a faulty voltage regulator and bad battery. After replacement of the regulator and a new battery install everything seemed to be working just fine.

Until.....that is, this afternoon tooling home up the Interstate in 100 degree temps with the AC on full blast we hit a little bump in the road and almost immediately I am blasted with super hot air coming from the vents. After 10 or 15 seconds it began to cool back down but it took a minute or two for the AC to overcome the sudden furnace blast and get back to normal cooling temps at the vent outlets.

I figure, either I have a loose electrical connection on the monovalve that briefly came loose or the monovalve is mechanically weak and the jostle allowed flow through the heater core for a short time.

pawoSD · #7 08-23-2007, 09:53 PM

On our 300D it has .5 volts on the wires to the monovalve...at all times, when the car is on or off, no matter what setting the klima is in....etc....even when its "off". So my solution was, since the A/C doesn't work, I quick spliced the connector to the monovalve to the one for the a/c compressor....so now when you want "cold air" you set it to cold and choose a non-ec mode, and it closes the monovalve. Works perfectly.

For heat you choose "ec" and it opens and all of Mt. Doom's heat comes in the cabin. None of the vac flaps work either, so floor, dash, and defrost all get pretty good airflow...especially on high, it has amazingly powerful heat!

I did have to replace the diaphragm in the monovalve as well, it was completely shredded. Only cost $34 to replace and took about 5-7 mins. Easy.

So it is very "rigged" but gives normal air and heated air reliably....and thats all we need....its going to be my sister's "driver" so we don't care all that much anyways....