heater vacuum actuator

65 Tux park with F-head. heater blows HOT and wonderful, but pushbuttons fail to actuate doors between heat and defrost. If I push the defrost button and manually "nudge" the actuator lever for defrost, it will slowly actuate, and once it's in place, it is strong! I can't pull it back manually until I reset the buttons. The heater door is another matter. I can manually actuate the door into the position I want, and get no help from vacuum assist, and it is NOT strong once in place. I can move it as I want it. I guess my question is . . . is there a well-known place of failure I should start with? Assume vacuum assist is bad? Or assume pushbutton rack is bad? I know I have vacuum, but I haven't tested to see how much. What is acceptable vacuum? About 14 inches?

 

If you look at both actuators you will see the return spring on each one. The spring pulls the door shut. The door shaft should be free of rust and crud. I put a little grease on mine. The vacuum will fluctuate with throttle response. 14 inches is enough to open the doors if they freely move.

 

Check the hoses going from the heater control to the actuators, you may have a vacuum leak.

 

Thanks guys! I'll give 'er a rip . . .