87 dodge d100 can't get defroster diverter to work

[peach8598]

Can't get defroster diverter to work, stays in vent position. Has heat but will not switch positions.

[GHS]

I you have the cable operated version, the cable anchor probably came loose. If you have the vacuum operated heater, the likely cause is a leaking vacuum hose or broken fitting. The plastic gets old and they break quite easily.

[Chump]

#9 is the door that switches air flow from vent to defrost, it is controlled by vacuum to #12.