The voltage to the monovalve should be at least 11 volts and the resistance should be between 11 to 19 ohms.

I had a problem with heat coming out all the time too. I tested the mono valve in question and it measured the proper resistance. I still thought it was the mono valve so I took it apart and the little diaphram inside was busted and coolant was going where it should not go. The monovalve was the problem.

I took the mono valve out of my 92 300E and put it installed in the 92 300TE after removing the one I took apart. The monovalve was the problem, even though it had the right resistance.

I suggest you take one of the monovalves apart and I think you will be able to push the little brass valve thing (for lack of a better term) inside down to keep it in place, that way hot coolant will not get to the heater core in the evaporator box.