Heater & defrost problems on an A/C car

[histoy]

I have a '68 Charger equipped with a factory A/C unit that works GREAT... better than the one in my '05 Chrysler 300.   The problem I'm having is with the heater and defroster.  If I push either of these buttons the fan won't work.  I hear a door close for the defrost, but the fan doesn't run in any position.  If I push the button for A/C, then the fan will run and the defroster works.  If I push the A/C, and then the heater button, I get cold air blowing from the A/C.   Should I check the hose routing on the vacuum switch, or something else? 

[John_Kunkel]

The pushbutton switch is bad; it has to send power to the fan speed switch in all modes (except OFF) and it isn't doing that.

Current P/N for the switch is 3895033.

[BigBlockSam]

impressive   Mr. Kunkel