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1973 - 1979 F-100 & Larger F-Series Trucks Discuss the Dentsides Ford Truck

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Old 06-25-2012, 10:40 AM
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New blower motor won't come on?

My blower motor went out a few months ago (at least I thought it did). It would work but squeal sometimes and not sometimes then it got to where it would only come on sometimes, then it wouldn't come on at all. So I tore into it yesterday to replace it. Took me almost 2 hours and some cut up hands from the evaporator, but I got it done. Crank the truck up hit the A/C and the freakin blower motor doesn't come on So, I didn't test stuff with a multimeter but I did get out the test light I checked all the fuses and I checked the wires hooked to the blower motor relay, all three of them made the test light come on. Does this mean my relay is fine and the problem is somewhere else or that the relay is bad? It was getting late so I didn't pull the evaporator cover back off to check the orange wire to the blower motor itself for power, I'll do that today if ya'll don't think I should just replace the relay and that'll fix it.

From stuff I read while searching for answers it seems like it could either be the relay or the resistor thats mounted in the duct?

What do ya'll think??

77 F100 302 with Factory A/C
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Old 06-25-2012, 11:02 AM
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Usually, if the resistor is bad, the blower will still have high speed. My money would be on a bad relay. It's buried up behind the glove box.
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Old 06-25-2012, 11:10 AM
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Ok cool thanks, yea I don't have any speed on the fan, it won't do anything. Good thing I don't have a glovebox. LOL it's been gone for years. Open the door and instant access to under the dash.
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Old 06-25-2012, 11:16 AM
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I bought a '77 F250 brand new (wish I still had it). In the four years I had it I replaced the relay (Ford calls it a safety relay) twice and it was bad again when I sold the truck. Still had the original blower motor.
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Old 06-25-2012, 11:24 AM
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I'm sure the relay is my problem, makes all the contorting I had to do, the colorful language, cut hands, bumps on my head from hitting the dash, and scraped knees on the concrete useless, except I know now I have a new blower motor that won't squeal when I turn it on.

To anyone who plans on doing this getting the squirrel cage off/on the motor is a PITA without a long allen wrench! This is a job where having the correct tools makes the job much easier.

EDIT: I had read in another thread during my searching that a guy had used a jumper to get around the bad relay. I figure this isn't the safest thing to do, but in order to test it out which of the three wires should the jump be between?
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Old 06-25-2012, 11:32 AM
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--EDIT:-- On the relay, there are three wires. There should be a large orange wire. That is +12v DC hot STRAIGHT from the battery. One of the other wires is a +12v, but ONLY when the AC controls are turned on. The last wire is the output which runs to the motor. Jumping from the larger orange wire to EITHER of the others will not hurt anything, since the relay grounds to the dash/firewall. So, you can try one, then try the other. Shouldn't be able to fry anything by doing it. At least, I think not, if my memory serves me right! If you apply power to one, you should hear the relay click, assuming it's good. If you apply power to the other, the fan should turn on at whatever speed you have the fan switch set to.
--END EDIT--

Check the orange wire at the blower motor for power (with the test light).

If that's bad, then I would replace the relay, and re-test at the orange wire. It's entirely possible (but unlikely) that you got a bad motor.

The previous owner of my truck had the relay go bad...and rather than spend $10 to fix it, he did a total hack job and ran wires, stripped insulation, and just made it horrible. Then, the motor itself went bad. So, I had to replace the motor, relay, AND fix the wiring that was butchered.

Ugh!

Hope you get it working soon! It's been so hot on the east coast recently that I'm glad I bought a Jeep with a good AC system!

-Brad
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Old 06-25-2012, 11:42 AM
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If it hadn't been getting late and I wouldn't have had to pull the cover off again I would have checked the orange wire yesterday. Looks like I'm going to have to order the relay neither Autozone nor Advance are showing they keep them in stock.
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Old 06-26-2012, 09:37 AM
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I'll give the short version first.
It was a bad ground the fan wasn't grounded so it wouldn't come on. YAY no money fix!!

Long version.
I started at the the relay plug testing wires with the test light all of them were working properly, but when I used the jumper the fan wouldn't come one. So then I take the evaporator cover off and unplug the fan wiring test it there with the light and juice is getting to there. Next spot I test is the wire after it runs through the grommet beside the evaporator, got juice there too! At this point I'm thinking I got a bad motor and I'm gonna have to take all this crap apart again. So then to test the motor I ran a wire from the constant hot at the relay plug for 12 volts and a temporary ground wire just to touch the bottom of the dash. As soon as I touched the ground wire to metal that fan come on!!! So then I know the ground is my problem. I fixed the ground and now I have nice cold A/C blowing on me again!!

And this thing obviously blows much harder than my old motor because when I put it on high all kinds of dust and debris came flying out the vents. Plus I can just feel it blowing harder than it ever did before. Its a 4 seasons motor from Advance, they were actually the cheapest place I found it, it was only $21.99.

Thanks for the help and suggestions, maybe this will help someone else too.
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Old 06-26-2012, 10:28 AM
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