Blower motor won't switch to high. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

1985-GMC · 02-14-2012, 12:32 AM

This is about to drive me nuts trying to figure this out, this is on my 78 with A/C. With two old relays I have the blower motor works on idle, low, med then kicks back down to the idle when switched to high. Ive bought a new "USA" relay thinking that was the problem but this one does the same except it blows the fuse when switched to high. I pulled the cap off one of the old relays and the fan will blow full speed when I manually switch it with my fingernail. I also swapped out the blower motor for another one even though the old one was still good. I pulled the switch apart to check it out then cleaned, greased and put it back together; it looks new inside. The resistor looks good and I even went ahead and tried out another one I have, same result.

So... I have 5 wires on the plug to the relay, when switched to med the big red wire has power, the small blue wire has power, the small black wire is grounded to the firewall along with the fan (I checked it), the small orange wire has nothing, and the big purple wire going out to the fan of course has power. If I jump power from red to blue it kicks the fan to full speed, if i jump power from red to orange it stays the same...

Im going to go ahead and pick up a new switch from the parts store tomorrow if they have one, and what do yall think about the new relay? Good, bad, wrong part? And what about the orange wire? Thanks in advance for any help!

jtj143 · 02-14-2012, 12:36 AM

The blower motor on my '71 does the same thing...I suspect it's the switch, but I have not tried to diagnose yet. Interested to hear what you find.

bigwheel15 · 02-14-2012, 02:12 AM

I had that same problem when I swapped heater boxes on the firewall. Turns out I didnt have a ground connected.

1985-GMC · 02-14-2012, 01:16 PM

Well I already made sure the ground was connected and not corroded. Do you think the new relay housing needs to be grounded? Unless you mean another ground under the dash?

What wire runs to the fuse box?

Stoney · 02-14-2012, 02:37 PM

I had that same problem. Mine was the connector to the relay. The red wire terminal was melted.

1985-GMC · 02-15-2012, 12:59 AM

Well I didn't make it to the store today to get a new switch. Does anyone else have any tips?

02-14-2012, 12:32 AM	#1
1985-GMC Chevy Enthusiast Join Date: Jul 2009 Location: Canyon Lake Texas Posts: 2,024	Blower motor won't switch to high. This is about to drive me nuts trying to figure this out, this is on my 78 with A/C. With two old relays I have the blower motor works on idle, low, med then kicks back down to the idle when switched to high. Ive bought a new "USA" relay thinking that was the problem but this one does the same except it blows the fuse when switched to high. I pulled the cap off one of the old relays and the fan will blow full speed when I manually switch it with my fingernail. I also swapped out the blower motor for another one even though the old one was still good. I pulled the switch apart to check it out then cleaned, greased and put it back together; it looks new inside. The resistor looks good and I even went ahead and tried out another one I have, same result. So... I have 5 wires on the plug to the relay, when switched to med the big red wire has power, the small blue wire has power, the small black wire is grounded to the firewall along with the fan (I checked it), the small orange wire has nothing, and the big purple wire going out to the fan of course has power. If I jump power from red to blue it kicks the fan to full speed, if i jump power from red to orange it stays the same... Im going to go ahead and pick up a new switch from the parts store tomorrow if they have one, and what do yall think about the new relay? Good, bad, wrong part? And what about the orange wire? Thanks in advance for any help! __________________ Tony 1985 GMC K2500 restoration Project: Rust, White & Blue 1989 Chevy R3500 CC Cummins & 4X4 swap some day... 1989 Burb (D60, 14BFF, 12V, NV4500, NP205, 37" tires in progress) Last edited by 1985-GMC; 02-14-2012 at 01:02 AM.

02-14-2012, 12:36 AM	#2
jtj143 Registered User Join Date: Jun 2010 Location: Dotsonville, Tennessee Posts: 194	Re: Blower motor won't switch to high. The blower motor on my '71 does the same thing...I suspect it's the switch, but I have not tried to diagnose yet. Interested to hear what you find. __________________ '65 GMC Suburban 4X4, '71 GMC 4X4 LWB - The Yellow Eyed Monster, '86 C10 Silverado - Oldest Daughter's Pickup, '88 S15 GMC Work Truck, '95 GMC SLE 4X4 - Second Daughter's Truck, '99 K1500 GMC Suburban Road Trip Machine, 2000 C2500 W/T Utility Bed Work Truck, '03 Silverado - Wife's Grocery Getter

02-14-2012, 02:12 AM	#3
bigwheel15 Registered User Join Date: Feb 2010 Location: Fort Worth, TX Posts: 727	Re: Blower motor won't switch to high. I had that same problem when I swapped heater boxes on the firewall. Turns out I didnt have a ground connected.

02-14-2012, 01:16 PM	#4
1985-GMC Chevy Enthusiast Join Date: Jul 2009 Location: Canyon Lake Texas Posts: 2,024	Re: Blower motor won't switch to high. Well I already made sure the ground was connected and not corroded. Do you think the new relay housing needs to be grounded? Unless you mean another ground under the dash? What wire runs to the fuse box? __________________ Tony 1985 GMC K2500 restoration Project: Rust, White & Blue 1989 Chevy R3500 CC Cummins & 4X4 swap some day... 1989 Burb (D60, 14BFF, 12V, NV4500, NP205, 37" tires in progress)

02-14-2012, 02:37 PM	#5
Stoney Farm Truck Join Date: Aug 2006 Location: Jersey Village, Texas Posts: 547	Re: Blower motor won't switch to high. I had that same problem. Mine was the connector to the relay. The red wire terminal was melted. __________________ 1969 CST/10 1984 K5 Blazer 4x4 2016 Dodge Ram 2500 4x4 Mike Jersey Village, Tx

02-15-2012, 12:59 AM	#6
1985-GMC Chevy Enthusiast Join Date: Jul 2009 Location: Canyon Lake Texas Posts: 2,024	Re: Blower motor won't switch to high. Well I didn't make it to the store today to get a new switch. Does anyone else have any tips? __________________ Tony 1985 GMC K2500 restoration Project: Rust, White & Blue 1989 Chevy R3500 CC Cummins & 4X4 swap some day... 1989 Burb (D60, 14BFF, 12V, NV4500, NP205, 37" tires in progress)

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