ACC questions

[1980sel]

So my servo is starting to act up more then usual...it's stuck in cold mode...I plan on just putting in a manual heater valve, but my question is with another qirk of the system. If I've got air blowing...doesn't matter which setting or hot or cold....and I get on the throttle it shuts off until i let up on the throttle...the other thing is if it's below say freezing it won't turn on at all unless I fist choose deforst and let it run for a few minutes then I can choose another setting and it'll behave the rest of the day...like something has to warm up first. Figure if I'm digging into it I might as well try to fix these problems as well. Nothing looks messed with and all vacuum lines look healthy. Any ideas on where to start?