Opposite problem of the full on heat problem
 

WHen the heater is on the hottest temperature it usually blows really hot. Tonight i had it cranked on hot and it was warm but not as hot as it usually is. WHen i hit the defrost button it gets super hot again but only when i hit that defrost buttong. Any suggestions? Thanks

Heater control valve is sticking or the vacuum line is disconnected.

located right behind the cam housing,.

AFJuvat