Testing '72 HVAC Switch?

[clhyer]

Howdy all,
Working on my '72 Duster. I have power to the hvac switch, but the fan motor does not work. It is a new blower motor. I've checked the FSM but it has no guidance on how to test this switch. Can anyone shed some light on the subject for me? I hate to spend $100 at Year One on a new one if I don't have to...
Thanks,
C

 

[70Duster440]

Have you checked the blower motor resistor?

With a test light or a voltmeter you should have power, at the very least, on the circuits marked in yellow.

If the HVAC switch is bad, they're still available through your local parts store: http://www.autozone.com/autozone/pa...1?filterByKeyWord=ac+switch&fromString=search

 

[clhyer]

Thank you 70Duster440!
My experience with the blower motor resistor is that the fan only works on high when they go bad. I may go ahead, though, and replace it if I can find one. These parts are probably 40 years old!
And thanks again, for the link. When I pop in the '72 Duster nothing comes up. I will just order one for a '70 Duster.:cheers:
C

 

[70Duster440]

No problem. You can at least rule out a bad HVAC switch by probing the various circuits, though I don't know under what conditions you'd see power on C7A. You could also probe the resistor and switch terminals to see where do you or don't have power with the key on.

 

[Oklacarcollecto]

Darn, a real NOS Mopar one just sold on eBay for $43.65.

http://www.ebay.com/itm/400251407458?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

 

[clhyer]

It did turn out to be a bad HVAC & vacuum switch. Thanks again 70Duster440 for steering me in a good direction. Right now the fan works, not sure if it is working correctly though. All the vacuum pods work but the defroster door is hanging up.
I did pull the blower motor resistor and looked at it. It looks good - which is good because I could not find a replacement. Man, was that a tight place to get up into to get that out!
C

 

[70Duster440]

Glad you got it narrowed down. The electrical switches built into those vacuum switch units are pretty crude and if it ever got overheated (via a siezed fan motor) then they won't keep working well.

You might disconnect the "sticky" vacuum pod and work the door by hand to see if it's stiff through it's entire range or just when it's closed. They have foam attached to them which is most surely rotted by now. That may be what's causing it hang. Unfortunately, you'd likely have to pull the box and disassembly it to fix all that. Detroit Muscle Technologies has the resto kits for them.