Recently changed-out heater core in 77 Pontiac TransAm. All is good except have high heat all the time. Took the driver-side seat and console out today to check function of heater/AC controls. Car has AC but is inoperable. Sliding the heater controller on the dash left/right appears to open/shut the inside heater door in the heater case assy. All pneumatic tubing is terminated properly -- positioning the heater/AC selector from OFF/NORM/BILEVEL/VENT/HEATER/DEFROST appears to change setting of outside heater case door. Heater door control latch is OK.
After 10-15 minutes run time have high heat at the heat box even with heater selector in OFF position or in any position.
Any comments or direction to relevant tech info on this topic would be welcome.