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on my 79, I finally got the A/C fixed yesterday after years of living without it. Drove it home from the shop with the A/C on and now the blower motor isnt working. I'm thinking it's the relay on the firewall and here's why. I get 12 volts coming into it on one of the wires that plug in on the top, but the purple wire that goes from the relay to the motor doesn't have any power on it. This is with the key in the on position and fan set on high in the vent mode. Shouldn't I be getting 12 volts at the purple wire coming out as well? Can't even get my hand to the connector at the motor itself without a moving the overflow tank, so I haven't checked for 12 volts there, and am trying to avoid it if I can. What say you CF all knowing ones? Does it sound like a bad relay?
Wilcox has a great diagram and video of testing relay and switch. Make sure good ground on motor. I had to upgrade my 79 blower ground to larger wire. Helped a lot.
Possibly your motor died. Jump power straight to it see if it runs with full 12v
Last edited by speedreed8; Aug 26, 2020 at 09:06 AM.
Wilcox has a great diagram and video of testing relay and switch. Make sure good ground on motor. I had to upgrade my 79 blower ground to larger wire. Helped a lot.
Possibly your motor died. Jump power straight to it see if it runs with full 12v
I'd love to jump 12v direct to the blower motor, but I don't want to have to take the overflow bottle out just to reach the connector. I can't get my hand down in there with the bottle in the way.
I'd love to jump 12v direct to the blower motor, but I don't want to have to take the overflow bottle out just to reach the connector. I can't get my hand down in there with the bottle in the way.
unplug the connector on the relay and put 12v to the purple wire
Ok, put power to the relay end of the purple wire, no go. Took the radiator overflow out, pulled the purple wire off the blower and I do have 12v at the motor, so off I go to hopefully get a new motor at NAPA. What is strange though is that I saw 12v on the next to high position, but when the switch is in high position, I only saw 4v. Any reason why? Possibly, I wasn't doing a good job of grounding? I was touching the ground lead to a valve cover bolt.
High speed relay may be kaput.
If your changing the blower motor, consider the C4 unit. Very good upgrade. You just need to make a spacer. Search for the threads.
I tried the same tests on the blower on my 69. Removed the blower to get replacement numbers (original blower) and decided to give it one more test. This time I hooked negative of a 12 volt battery to the fan base and positive where it should be on the motor. Motor roared like it was new. The plate was rusted where the ground is attached. Sanded the contacts down and put it back in. (Which was a giant pain in the *** on a 69. Have to disassemble into two parts through gills and then get each one past poa valve etc.). Works great now. Motor needs a really good ground to function!!
Hope this solves the problem. Couldn't hurt to try this test.
blower motor stopped working
