BenzWorld Junior Member
Date registered: Dec 2008
Vehicle: MB 1986 420SEL, 1989 Toyota Supra, 1963 Dodge MaxiVan, 1992 Ford350RV,
Location: Lavonia Georgia
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No Heat! May be the monovalve.
I have owned an 86 420 SEL for five years, and the first cold day we had no heat, I researched and the 'mono-valve came up several times. Not sure it is the same on your car, but it is located in the firewall bay near the battery.
After learning the price I almost choked. Ahh Ha! Ebay! found an oem unit and won the bid at $10.00
The mono valve "should be multi valve' is an electrically actuated plunger valve similar to a trumpet valve. As the need for heat is required the plunger reroutes the water to various areas and also controls the amount of water flow.
The interior climate system uses an air recirculation circuit with several sensors and controls under the dash.
Time to install, After looking at all the hoses and deciding that there would be a great opportunity to break something to get the valve out, I decided to first remove the top. Just three screws. I removed the wired climps and just pull out the inner components. The plunger was gunked up. I cleaned it and the inside cylinder. I probably could have returned the used unit, but just decided to separated the new unit and drop it into the old housing. iI reinstalled the screws and wires...
Vola! heat in all locations.