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Old 12-29-2018, 09:40 AM   #1
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Join Date: Oct 2018
Location: Malvern Ohio
Posts: 32
Blower motor fan stuck on high- Buzzing from relay

I need help- I've read and read and it seems like veryone has the opposite problem.

Working on a 72 k10 w/ ac
With key on, blower motor relay plugged in fan comes on low w/ no buzzing from relay, then med with buzzing noise from relay, then high w/ no noise from relay and then fan switch and key will not turn off blower. If I unplug the sm 18 orange wire from relay it shuts off.

If I leave the 18 orange wire from the relay unplugged all speeds work fine and it shuts off with the switch- basically it all works the way it should.

Should the 18 orange wire not be connected? There is a plug on the relay for it.

If I test the orange wire while unhooked from the relay it shows voltage directly related to the fan speed.

I tested switch and it is good.

The relay has a good ground, I even ran a ground straight to the battery to test it.

For reference- My truck has a purple wire running to the fan motor and I do have a wiring diagram. The 18 orange wire runs from the relay to the fan switch.

I've messed with this for hours and read as much as possible. If anyone could provide some insight I'd sure appreciate it!
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