Heater control questions

[Roc87]

Everytime I switch from "off" to "vent" there is a very loud "Pop" from behind the dash, as if the flapper is stuck until it gets enough vacuum to open it (Close it?) is there something to grease or spray wd40 on to solve this??

 

[Roc87]

 

[zam70]

Not really - The main diverter flap commonly pulls out of it's hinge point (think peg & groove)
You are probably hearing the axle (peg) popping in and out of its slot.
You might check the cable behind the glove box (drop the glove box door all the way open so you can see behind it - look to the left)
those also will come loose as well.

 

[Warp Six]

Mine has done that for the entire 8 years I've owned the car. It sounds like the door is a little sticky, and it takes a sec to build up enough vacuum to move it, just like you said. It still works, so I don't worry about it.