'89 300SE weird HEAT, HELLLPP!!!

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Ok, now I'm frustrated. Here is the issue that started about 45 days ago. I mostly get heat while idling, but usually after few minutes it gets cold.. When I'm driving I usually loose heat. Its not the loss of air...the fan blows nice and steady, its the temperature of the air that is the problem...it gets cold!

I have replaced the monovalve TWICE. I have replaced the climate push button dash unit. I have replaced the vacuum unit with all the vacuum lines. I have replaced the radiator. I have replaced the thermostat....she runs just over 80*C..... It still acts the same.

What controls the temperature? Is it the monovalve? Is it closing for some reason and turning off the hot water? What would cause this?

If I put 12volts to monovalve leads I can hear/feel it clicking open/shut

I am at a loss and getting very frustrated and COLD......I hope someone can throw me something!!