I've just got this 86 SDL back on the road and having a slight problem finding one of the problems.
I have replaced the CCU and also the klima, the A/C system is fully charged and working, however, it appears that the monovalve is full open. Now, when we installed this engine, we did the acid wash and thoroughly flushed the system, then rebuilt the monovalve, and everything seemed fine for a short while.
Then came the heat. At idle, (with the A/C not working), the heat would be like a blast furnace. When moving down the road, it was not quite as hot, but still hot. When the A/C was hooked back up, the heat would equal or slightly best the cooling temperature. The blower motor seems to work at various speeds, and the aux heater pump feels like it is working.
A clamp on the heater hose lets the A/C blow really cold air.

Suggestions where to start?

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87 300SDL - 215K Miles !!
99 F-350CC Dually PSD - 190K
86 300SDL - 189K
All on B-100