Hey all,
79 f100 AC truck, AC is missing the comp and some other stuff but that's not my issue.
When i got the truck the motor was blowing really weak. I cleaned what i could out the flap but then the motor just stopped doing anything.
I know it has the red/ black wire to the fan but what i need to know is what wire goes to the fuse. I tested the port and my light didn't go on, fuse looks solid but I still need to test it (got side tracked with a fuel leak) I know it would have power with the key on but it shows nada
I have a volt meter but not sure how to test for that other than continuity
I found this diagram and honestly i get a lot of it but if someone could explain it a bit more it would help me know what to test. I have a new motor just not looking forward to that bear of a job...lol

Does any of the wires actually go out to the solenoid or voltage reg?
Thanks!

 

the orange wire comes from the fuse panel (fuse 3) to the AC mode switch. When you slide the mode switch away from the off position the blower motor switch is then energized. Putting the blower switch on High bypasses the blower motor resistor so assuming your fuse is good, AC mode switch is good, blower motor speed switch is good and all wiring, you should get 12v at the blower motor connection.

You can also run a quick test by unplugging the blower motor and connect 12v directly to the motor to see if the fan motor is good.

 

Something else to think about..... Mine was very weak as well and i removed the switch and cleaned all of the contacts. Since that it blows great!

 

Thank you for this. When i was under there i noticed a loose orange wire, which i assumed was for the aftermarket stereo someone put it (usually for illumination) I am gonna double check it now see if for some reason it was disconnected.


Yeah judging by how not clean Burt is I am guessing they need a good cleaning!

 

OK so after a friend and I looked it over a few things we noticed
Blower motor work with 12v directly
Orange plug was plugged into the red plug here shown with the green arrow and the purple was where the smaller plug went to. Once we did it like this we had full blower speed control but no selector control. We then tried connecting the 2 other orange plugs and had minimal blower speed no speed control and again no selector control. I am thinking possible bad selector switch

NOW we also spotted these 2 plugs *circled in red* and have no idea what they go to:


Thoughts?

 

Found this image from the vintage air site removal video showing the wires how they should be it seems.

I thought it was the switch but Rich suggested making sure nothing else important is missing since some of the AC system was removed (vacuum line etc)
I do want to add it is stuck in Defrost mode and has 0 reaction regardless of position of the switch

 

The lower red circled wire with the green plug and 2 wires is the OEM radio power. And BOTH wires are HOT, the ground comes from mounting the radio in the bracket with the rear mounted support arm.

Check the other single wire bullet plug right by it for constant 12V or 12V keyed power. If constant 12V it might go to the cigarette lighter. It could have a male plug then a 90* plug to go on the cig lighter back single stud. This below if the set up for the lower/bottom switch (mode control lever). The top one is the temp control lever as they are mounted in the bracket.



The underside of the enviro control panel. Broken switch stud and bottom part falls off on the R/H side.

 

UPDATE:
Plugged the orange from the blower switch to the red to the motor, then the orange from the harness to the orange from the plug as shown in my last picture and absolutely 0 power to the fan as in nothing happens at all. So i am not sure what could be busted...
We know the fan works wires differently and with 12v direct. So where do i go from here?

 

In reading through all the posts on your blower issues, I yet to see any mention of the blower relay. I have a 1976 F350 supercab, 460/C6 with factory air. When I encountered similar blower issues as you have been discussing, and tearing into the wiring, switches, etc., and finding no real issue, I discovered the blower motor relay mounted on the bottom of the dash near the glove box. It's slightly visible from the driver's seat. I'm the original owner of this truck, and every time I've encountered a blower issue--three times--the problem has always been the blower relay. It's an easy item to check; just remove the plug and supply 12v to the appropriate terminal on the relay, ground it and listen for the relay to click. No click, then the relay is not working. The relay is inexpensive and available at just about any autoparts store, Amazon, Ebay, etc. The relay would be where I'd make my next troubleshooting effort.

 

Thanks for the info, i wasn't sure if there was a relay involved. is it where the plug for the blower (red/black wires) plugs in? ill have a look around that area and see if i can spot it.

 

You do not need to expose any of the dash mounted heater/AC/blower controls. The blower relay is easily accessible from the passenger side. Place your hand against the bottom lip of the dash, just below the glovebox. Slide your hand, with fingers slightly extended, toward the center of the truck and you will contact the relay just to the left of the bottom of the glovebox. It’s attached to the bottom lip of the dash with a single sheet metal screw. If I could figure out how to post pictures, I’d send you a pic.

 

I just did what you said and while i did it fast I didn't feel a relay at all. I would not be surprised if it was removed if im honest. I'll have another look after dinner

 

1976 F series blower relay

 

So it seems that in 1979 the blower motor relay was no longer used Not sure why but then again when does Ford make sense with changes lol.
I am gonna list what i know again for anyone skimming through. I do appreciate you trying to help

Fuse panel #3 shows no power with key off or on, Not sure if i grounded my test light proper.
Anyone know what side of the fuse top or bottom will be the power side?
Fuse is good has continuity
Straight 12v the motor works
With the wires swapped orange from harness to red directly i get full blower but it shuts off at low. No direction control which could be a bad line OR ac selector switch.
With the other 2 hooked together weak blower motor, again 0 control from the selector switch
Set up normal 0 power to blower motor and obviously no selector control (seems to be a theme) though again since the AC was removed they could have disconnected a vac line somewhere.

The hunt continues. I am gonna pull the switch plug and see if the wires have power and check if the switch has continuity.
Would i want to test ohm load like a gas tank sending unit?
I feel it has vacuum as when i push the door open at the pass footwell gently, i can hear a air sound.

 

So what was the out come of this issue? Did you did the problem?