C10_Blackie
Full Access Member
- Joined
- Jan 2, 2024
- Posts
- 91
- Reaction score
- 187
- Location
- Seattle, WA
- First Name
- Rob
- Truck Year
- 1981
- Truck Model
- C10
- Engine Size
- 350
Just wanted to get this out there in case anybody else comes across this problem. Originally the blower on my 1981 C10 Silverado would only work on the first three speeds and never on high. I heard that this often is because of the high speed blower cutout relay being bad.
Without starting the truck, I checked the fuses for luck and then went under the hood. First thing I found was that the big red wire that goes to the relay had been cut cleanly. WTF? OK, so I put that back together and checked the resistor while I was at it, which seemed to be providing normal resistance.
So maybe that's all I needed to do. Turned the key to ACC and nothing. Started the truck, and nothing at any blower switch setting. Checked voltage at the resistor while moving the switch and got different values. Jumped the red and purple wires at the relay and the blower worked at full speed. So assumed the relay was bad.
Went to O'Reilly's, got a new relay and replaced it. Nothing - no blower whatsoever. Gave up - decided that there was something I just wasn't getting and resorted to my friendly local auto mechanic (who is excellent - Do-Rite in Kent, WA).
Turns out I did make mistakes, but also turns out that I never would have figured this out on my own. One big mistake I made is that I never went back and checked the fuse - turns out it was melted and its a miracle that it didn't damage the fuse block. Found out that my aging blower motor - although it appeared to work fine - was drawing massive amperage when it first started at high speed and would have fried fuses all day long and I don't think I ever would have realized that there was an issue with the blower motor.
Also - surprise - it turns out that the relay I had was good and that the one O'Reilly's sold me was defective. So that, along with the fuse, would have muddied the waters for who knows how long had I kept at it on my own. I'm not an experienced mechanic and this truck is a retirement project for me.
Solution was to swap the original relay back in, return the "new" relay to O'Reilly's and replace the blower motor with a new one. Now everything works great and the truck now heats up good and will heat up even better once I take a look at some of the ducting. Yay.
So be warned: old motors can work just fine but can start drawing so much amperage on startup that it can mess up the works. Maybe most of you already know this, but if I had found this thread when I was doing my research it might have saved me some grief so I thought I should put this out there.
Without starting the truck, I checked the fuses for luck and then went under the hood. First thing I found was that the big red wire that goes to the relay had been cut cleanly. WTF? OK, so I put that back together and checked the resistor while I was at it, which seemed to be providing normal resistance.
So maybe that's all I needed to do. Turned the key to ACC and nothing. Started the truck, and nothing at any blower switch setting. Checked voltage at the resistor while moving the switch and got different values. Jumped the red and purple wires at the relay and the blower worked at full speed. So assumed the relay was bad.
Went to O'Reilly's, got a new relay and replaced it. Nothing - no blower whatsoever. Gave up - decided that there was something I just wasn't getting and resorted to my friendly local auto mechanic (who is excellent - Do-Rite in Kent, WA).
Turns out I did make mistakes, but also turns out that I never would have figured this out on my own. One big mistake I made is that I never went back and checked the fuse - turns out it was melted and its a miracle that it didn't damage the fuse block. Found out that my aging blower motor - although it appeared to work fine - was drawing massive amperage when it first started at high speed and would have fried fuses all day long and I don't think I ever would have realized that there was an issue with the blower motor.
Also - surprise - it turns out that the relay I had was good and that the one O'Reilly's sold me was defective. So that, along with the fuse, would have muddied the waters for who knows how long had I kept at it on my own. I'm not an experienced mechanic and this truck is a retirement project for me.
Solution was to swap the original relay back in, return the "new" relay to O'Reilly's and replace the blower motor with a new one. Now everything works great and the truck now heats up good and will heat up even better once I take a look at some of the ducting. Yay.
So be warned: old motors can work just fine but can start drawing so much amperage on startup that it can mess up the works. Maybe most of you already know this, but if I had found this thread when I was doing my research it might have saved me some grief so I thought I should put this out there.
