Heat/AC Confusion

[louser151]

My '66 Coronet Wagon is a factory A/C car, and I have power to the controls, and power to the heater resistor. The blower motor fan kicks on with A/C and Max A/C, and the fan speed control works, but as soon as I hit the Heat, or Def button the blower motor shuts off and there is no power to the blower motor resistor. I am kind of lost. Any words of guidance?

 

[Sixpactogo]

It sounds like your heater A/C vacuum switch has failed. The plastic unit behind the push buttons.

 

[louser151]

So from the top pin to the bottom pin should there be continuity between the 2 in all modes? I have it in all except heat, so I bought a used one and same thing. Should I be looking for something else?

 

[Coronet67guy]

So from the top pin to the bottom pin should there be continuity between the 2 in all modes? I have it in all except heat, so I bought a used one and same thing. Should I be looking for something else?

Sounds like my 74 Charger. Let me know if you figure it out. I have blower motor blowing on max AC and AC positions, but nothing anywhere else. And I think my fan speed control only blows on high. I'm in the middle of getting AC back in the car and hope to get it all working correctly.

 

[Armycopter]

I am having the exact same issue with my 69 Charger. I will be watching this thread.

 

[beanhead]

Be aware that there are two feeds, from two separate fuses to the vacuum switch. So check those first and then verify all the connections are good. You really need a service manual to troubleshoot unless someone chimes in that remembers which wire colors go to which termination points, and which terminal should have power in 'heat' mode. (sorry I don't remember). And, some manuals have a separate A/C-Heat schematic in the A/C section, not with the other wiring diagrams. (That much I remember!)
What I would do is turn it on heat, and check for voltage starting at the motor and work my way back up the circuit to find where it's losing power.