Rick00,

I missed that this is a 124 car. Somehow, I originally thought you were working on a 123 with a late Climate Control, I guess because that's what I automatically think about when I hear the term monovalve.

I replaced the monovalve on my 124 car last year thinking that was the problem. A waste of money. When I explored further I found that the pushbutton unit was not turning it off. If you disconnect a properly working valve on the 124, it will continue to flow hot coolant.

There are several ways to determine if the problem is too much heat or not enough cool. One would be to somehow cut off water flow. I believe you could clamp the hose leading to the valve without permanently damaging it. If you clamp it off and you then get cool air, then the problem is the valve or the pushbutton control unit.

Also, is this HOT air coming out? Is it hot when you first start the engine when cold? If it takes a little bit for HOT air to come out it's probably flowing hot coolant and that's your problem.

It also could be a combination of the two problems.

BTW, if the problem turns out to be the pushbutton control unit, make sure you check the auxilliary pump for current draw. It should not exceed 1.3 Amps, if it does replace it, or it will blow your new pushbutton control unit.

Best of luck,

------------------
Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles