1987 W126 ACC question
 

I need to bounce this question off the group here. I imagine this subject has come up in the past.
My ACC system is behaving strangely and I think I know what it is but I wanted some other opinions before getting the wrenches out.
Upon a cold (30 F) start up, as in the morning, I will switch the heat on and give the car 2-3 minutes to run before heading out.
The system will blow cold air and never (for 30 minutes of driving) switch to warm. UNLESS I shut the engine off and restart it. Then it immediately blows warm air.

What the heck is that?
Any ideas are greatly appreciated,

Rick