I'm still troubleshooting a non-working blower motor problem. I removed the glove box, disconnected what I belive to be the power lead to the motor and checked to see if there was any voltage at the plug--there was none for all switch selections (ignition was on). I belive it is the switch but I'm not sure. I know there is a resistor in the circuit between the switch and the motor but where is it located? I think there is a relay in the circuit, too; where is it located? If there is one, what's the part number?
Thanks

 

Didn't you just ask about this in another thread? Why start a new one where people can't see the history of what you've already done and what's been suggested?

Is there power *to* the switch? Is the fuse good?

The resistors are mounted in the ductwork. They aren't used with the switch in the "high" position, so if they're the problem, the fan will still work on high, just not lower speeds

 

Relay was used late '75 through '77 only. It's located behind the glove box.

 

I apologize for starting a new thread, but it's been my experience, after being a member of this forum for 14 years, that once a post gets moved off page 1, and there's only been 2-3 replies, then additional posts to that thread might not be seen again by anyone other than the original re-pliers. I sincerely appreciate all the comments/advice from all of you. My intent was to put it out there again, with a couple of new questions, to see if there might be some additional replies. I've heard others mention the relay, but I can't locate one in the online wiring diagrams. This is a wonderful forum, and has kept my fanny out of the fire on numerous occasions. There is an absolute wealth of Ford truck info stashed in the minds of you guys.

Thanks

 

No apology needed - just thinking if you posted in your original thread (bumping it back to the top), you'd get less repeat advice and it would be easier for people to see what had already been done rather than starting from scratch. To each his own though - we'll still try to help

 

Thanks, bkaul

 

Any time. If you want to find out if it's the switch, grab a multimeter and do one of two things:

1. Check whether there's 12V coming *to* the switch to begin with, then if so whether it's also getting past the switch
2. Check the resistance across the switch in various positions - when in L/M/H, there should be different pins with continuity; when off, there won't be any.

 

Thanks, I'll do that tomorrow. I hate working behind the dash.

 

You should be able to pull the trim panel out of the way and pull the HVAC controls out the front to get to the back of the switches. Even if you unplug them entirely and pull them out, you can (1) check the voltage at the connector with the ignition on - there should be a pin that's +12V, and (2) check the resistance across the switch with it unplugged. Better than contorting yourself to get up under the dash.

 

Great HVAC info...1979 F100 Air Conditioning

NORTH COUNTRY SPECIALTIES ®

 

I've confirmed that no power is getting to the plug that attaches to the blower switch, with the ignition on. There is power at the fuse panel (both sides of the fuse). I disconnected the power lead to the switch at the junction that's about 4 inches from the plug. It's a simple one wire push-pull connection. There was no power getting to this junction either.

I jumped from the the fuse panel (the 30 amp heater fuse) to the plug that attaches to the switch and the blower works fine. This truck's interior is in like new condition from having been garaged during it's 39 years of existence. There is no obvious wiring damage/corrosion behind the dash. I'm not sure where the next upstream junction is for this wire, so I don't think I'm interested in doing any tracing unless one of you guys can suggest an "easy" way to do it. I'm leaning toward running a new wire to the plug (10 awg wire with inline 30 amp fuse) from an ignition controlled source --any suggestions? Starter solonoid? I have the factory dual battery set up in my truck.

Just to remind everyone, it's a 1976 F350 supercab with 460 and factory air.

Here are a couple of pics that will give you an idea of its condition.

Thanks

 

Since there's already power at the fuse, running new wire from the fuse panel would be the easiest, I think, if you're going to go that route.

Nice looking truck!

 

Thanks, bkaul; I just sent you an IM.

 

here is a link with info about the relay that Mike mentioned:

https://www.ford-trucks.com/forums/1...thout-key.html

if it was me, I would continue troubleshooting and replace the relay if it is bad (as opposed to simply adding any additional wiring.

 

My 76 F250 had the relay and it was a factory AC truck as well.

It almost looks like a horn relay. A small metal rectangle with a mounting tab. It was located under the glovebox area, bolted to the bottom of the dash. I believe it was three prong.