Climate Control Woes

[StreetTripleR]

Hi! New to the forums here and I'd like to preface my problem by saying that this is my second W126 and both have bee the best cars I've ever owned. That said, summer is coming to a close and I thought it would be beneficial to try and figure out why my heat doesn't work.

Mid last winter I had to replace my thermostat housing because it was cracked and I replaced my thermostat while in there. Shortly thereafter, my car started to have overheating problems and my heat started acting funky. I have since fixed the overheating (fan clutch) but I still have the heat problem.

It started with my car blowing ice cold air out of the passenger side vents and the air coming out of of all other vents becoming a little cooler. After I eventually did a coolant flush when it became a little warmer, I lost all heat. Not sure if they are related but they certainly seemed to co-occur.

My situation now is a little odd. When it's a little chilly in the mornings and I run my heat it semi works on low but is useless when the fan is set to high. If it gets too cold outside I lose heat altogether. Months ago I pulled my mono valve and it looked ok but the screen was blocked. I ordered an MTC replacement and it did not fit so I pulled a mono valve and magnet off of a 560SEL at the junkyard. This did not fix the problem.

I also pulled off its ccu, thinking that my solder joints might be the problem, and no change. If I unplug the valve, no change either. I get ice cold ac in this heat so I would like to think that the valve is functioning. With the ac on my center vents also randomly seem to blow air and not, maybe engine vacuum related but not sure.

Another problem that may or may not be related is that my washer fluid boils off and I believe its coolant routing is part of the same system.

Not sure where to go at this point...buy a new mono valve insert? Any help would be appreciated and thanks in advance!