65 Dart Heater AC Fan Problem

Hello Members. On my 65 Dart Restoration, I have a problem which I have been unable to resolve. Using my push button controls for AC and Heat/Defrost, my fan functions when I am on AC and Max AC, but not on Heat or Defrost. I have three different fan switches, and I have tried them all with the same results. I have a new push button vacuum switch which I purchased from Classic. All of my vacuum hoses have been routed appropriately and double checked....the wiring as well. So I pose the question....what can be wrong? Does the car need to be running to produce vacuum at the dash vacuum switch? Could it be an actuator? I have no clue, so that is why I am asking. Thanks for the help on this puzzle. Much appreciated. sgrip65