heater problems 1991 420 SEL

[chad]

i have a problem with my heater, which is really a problem here in Colorado in the winter. when the car is first started, i can turn the heater on, and it will blow hot, provided the engine hasn't been revved up. i assume this is because at idle, it has full engine vaccuum, and when it loses some of that vacuum, it goes to blowing cold. you can only get it hot again by shutting off the car, and restarting it. at first i thought this might have been a problem with the climate control unit, now i am leaning more toward a bad heater control valve, or something else. any ideas? as Dr Evil said..."It's freaking freezing in here, Mr Bigglesworth."