A/C and Heater Vacuum Switch

[Jdkenned360]

I have a 1969 Dart with factory a/c and heat. I’m in the middle of installing an American autowire classic update wire harness which doesn’t take a/c into account so I made my own harness up from the oem circuit.

Back before replacing the harness I kept blowing fuses on this circuit so I’m not sure if I may have fried the vacuum control switch from a short.

So basically hears my question. The blower runs on max a/c and a/c only. I do not get power to the blower on heat or defrost. I’m assuming those little wafers inside are toast.

 

[1968DodgeDart270]

I have a 1969 Dart with factory a/c and heat. I’m in the middle of installing an American autowire classic update wire harness which doesn’t take a/c into account so I made my own harness up from the oem circuit.

Back before replacing the harness I kept blowing fuses on this circuit so I’m not sure if I may have fried the vacuum control switch from a short.

So basically hears my question. The blower runs on max a/c and a/c only. I do not get power to the blower on heat or defrost. I’m assuming those little wafers inside are toast.

View attachment 1715512598

The push button control chart indicates the blower should function in all positions except off. So I think the short answer is yes your switch assy is bad. However a table showing pin to pin continuity of the vacuum switch would help you know for sure. I'm also looking for that table... I bought a new switch and it seems to be sending power to the ac compressor when off is pressed. That cant be right. If you'd like to compare pin continuity on the phone, pm me.

Chris

 

[Jdkenned360]

I don’t have any A/C components under the hood yet so I haven’t setup the wiring for the A/C side at the moment. That will be a project further down the road due to cost.

I’m pretty sure the blend door slide shuts the temperature control slide off and on though. Mine clicks when I’m all the way on the warm setting of the slide. I do find it hard to believe that the push button control would send any power to that switch when on heat though

 

[Jdkenned360]

Sorry I forgot you mentioned it’s sending power when off. That doesn’t make any sense either, sounds like you may have gotten a bad switch? I didn’t find any electrical diagram for the vacuum control unit itself in the FSM

 

[1968DodgeDart270]

Sorry I forgot you mentioned it’s sending power when off. That doesn’t make any sense either, sounds like you may have gotten a bad switch? I didn’t find any electrical diagram for the vacuum control unit itself in the FSM

I created a truth table to document the switch functionality. You will be interested in the a/b/c section. Compare yours to determine if your switch is bad. Do me a favor and let me know what d-e is when switch is in the off position on your unit. Chris

 

[Mike69cuda]

Have you checked you blower resistor? High speed on ac is the only time the blower gets full 12 volts. All other speeds including high speed on the heat go through the blower resistor. Your switch may be ok.

Blower speeds are different on heat and ac for the same fan switch position.

 

[Jdkenned360]

I created a truth table to document the switch functionality. You will be interested in the a/b/c section. Compare yours to determine if your switch is bad. Do me a favor and let me know what d-e is when switch is in the off position on your unit. Chris

View attachment 1715516016

I’m not sure which part number my switch is, do you have both switches? I’m assuming you do with both tables?

 

[Jdkenned360]

Have you checked you blower resistor? High speed on ac is the only time the blower gets full 12 volts. All other speeds including high speed on the heat go through the blower resistor. Your switch may be ok.

Blower speeds are different on heat and ac for the same fan switch position.

Do you mean to try different speeds with heat and defrost? None of the speeds work on heat and defrost and low/end/hi work on max a/c and a/c

 

[1968DodgeDart270]

Do you mean to try different speeds with heat and defrost? None of the speeds work on heat and defrost and low/end/hi work on max a/c and a/c

The truth table I posted is only for the switch continuity. I made the truth table so I could compare my switches. One was new and one was the one that came on the car when I bought it. Continuity matched through a,b,c while pressing each of the 5 buttons. So I suppose they are not defective? I suggest you compare your switch to my data to determine if that part of the switch is ok. If you switch matches my truth table a,b,c I suggest you go after the resistors and the rest of the circuit as Mike69Cuda suggested.

My new switch was pneumatically different than the old one and I managed to get all my doors acting correctly with the new one. The manual was difficult to understand and I don't think the vacuum line numbering is correct. It was definitely a PITA... Chris