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Old 12-29-2018, 09:40 AM   #1
OhioPaul
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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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Old 12-29-2018, 09:43 AM   #2
OhioPaul
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Re: Blower motor fan stuck on high- Buzzing from relay

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Old 12-29-2018, 01:26 PM   #3
VetteVet
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Re: Blower motor fan stuck on high- Buzzing from relay

Do you have the anti-dieseling relay? If it sticks it may keep the fan relay powered as well as the fan switch and the resistor. Otherwise I would suspect the fan relay.


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Old 12-29-2018, 05:53 PM   #4
OhioPaul
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Re: Blower motor fan stuck on high- Buzzing from relay

No anti dieseling relay that I am aware of. I do not see a purple wire at switch as the wire diagram shows or 2 greens at compressor switch. Is it mounted in another location?
My original relay did this and so does the new one that I bought.
As I read it it shows power from fuse box to the 3 prong harness, I don't understand why the single 18 orange has power as well- It's like the relay is getting powered twice?
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Old 12-29-2018, 06:48 PM   #5
VetteVet
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Re: Blower motor fan stuck on high- Buzzing from relay

Quote:
Originally Posted by OhioPaul View Post
No anti dieseling relay that I am aware of. I do not see a purple wire at switch as the wire diagram shows or 2 greens at compressor switch. Is it mounted in another location?
My original relay did this and so does the new one that I bought.
As I read it it shows power from fuse box to the 3 prong harness, I don't understand why the single 18 orange has power as well- It's like the relay is getting powered twice?
I think whoever colored the wires used purple. Here is the uncolored version except for the orange wire.

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The green wires would be for the compressor clutch switch which fed by the anti-dieseling relay and the yellow wire off the fan switch. It can work without the AD relay if you don't have one.\
I don't have AC on my truck so I'm not sure where it is if the truck has one.
I will search some threads and see if anyone knows.

Here you go.
http://67-72chevytrucks.com/vboard/s...ieseling+relay
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Last edited by VetteVet; 12-29-2018 at 06:54 PM.
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Old 12-30-2018, 03:44 PM   #6
OhioPaul
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Re: Blower motor fan stuck on high- Buzzing from relay

What's the "loose connection" on the wire going into the switch? What does that mean?
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