Fan Speed - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ssjones · 06-07-2006, 05:50 PM

When I run my fan for my A/C I can not get the high speed to run. Any ideas? New switch and fan have been installed.

Thanks.

**Stocker** · 06-07-2006, 08:20 PM

I *think* there's a relay (under the dash?) that operates on the high-speed fan setting...

Longhorn Man · 06-07-2006, 09:34 PM

Yup, on A/C trucks there is a relay.

ssjones · 06-08-2006, 10:19 AM

Anyone possibly have a pic to know what I am looking for. Is this near the fuse panel? Thanks.

blazerparts · 06-08-2006, 10:21 AM

I think it should be on the firewall under the glovebox.

Longhorn Man · 06-08-2006, 10:37 PM

yeah, it is on the passenger side somewhere. I can't remember where though, it looks just like the metal one by the fuse box, but that one is for the horn.

**Stocker** · 06-10-2006, 03:30 PM

I am an idiot-- I don't understand anything computer related. I have a digital pic of the relay, it's in my computer, and I can view it in HP Image Zone -- but I have no clue how to get it to Photobucket so I can (maybe) show it here.

Sigh... It's behind the dash, to the right of the heater controls, near the lighter. Mine was just floating loose, possibly b/c it got in the way when fiddling with A/C ducting while replacing the glovebox many years ago.

It has a black cover, measures ~1' x 2", and is ~1 1/2" tall. The bracket has a black (ground?) wire attached. There are two electrical connectors -- a single with an orange wire, and a triple with blue, purple, and yellow wires.

I hope this helps -- sorry about no pic!

stope4 · 06-10-2006, 08:22 PM

On 71 and 72s there are two relays. One is attached to bottom of dash to right of ac controls. This is the antidieseling relay. (not really sure what it's for) The second relay is attached to under dash ac box on passenger side. This is the ac fan relay. It is between the passenger kick panel and the ac box. You may have to take glove box out to see it. There are four electrical connectors on the relay. Two wiring harness connectors attach to these. One of the connectors has three wirs and one connector has one. The wire connector going to the one prong is the high speed relay. Your problem may be as simple as this connector needing to be attached. I believe 67 - 70 has only the ac blower relay and it's similar to the one for 71 and 72 but may be attached somewhere else.

**Stocker** · 06-10-2006, 08:32 PM

Quote:

Originally Posted by stope4

The second relay is attached to under dash ac box on passenger side. This is the ac fan relay. It is between the passenger kick panel and the ac box.

Maybe not are all the same. Mine is as I posted above, and it is OEM and the wires are too short to have the relay situated anywhere other than within a couple inches of the cigarette lighter.

jhow66 · 06-11-2006, 12:46 AM

You can see it by looking up between the glove box and kick panel. this relay MUST be grounded. Take a jumper wire with clips and contect one end to relay and the other to ground. If your high speed works you have found your problem. ( there is a small black wire that is supposed to be attached to the one of the screws that mounts the relay to the ac box--if there is one there check to see if it is tight as these screws strip easy) If still does not work trace the large red (sometimes orange) wire back to the fuse panel to see if it is plugged in. This plug in gets loose and will heat up over time and corrode enough that it will loose connection. (check next post)

jhow66 · 06-11-2006, 12:56 AM

here is where it will plug in: this wire feeds high speed only--rest of speeds get the current through switch. (you can check your fan motor for high speed by removing wire from blower motor and run a jumper from motor to plus post on battery)

**Richard** · 06-11-2006, 01:16 AM

It has been a while since I looked at the wiring. I might be able to look it up later for you. One thing that comes to mind is how the fan speeds hook up. There is a resistor that is mounted in the air duct that actually controls the fans speed that has power going to it, but if I remember correctly the high fan speed has a straight wire that runs all the way back to the fuse panel. The reason this comes to mind is that wire was all hacked and not hooked up in my truck. after re-reading looks like I was beat on my explaination.

**Stocker** · 06-12-2006, 07:11 PM

I know this is a bit late, but with help from my daughter, here's a pic of the relay

06-07-2006, 05:50 PM	#1
ssjones Registered User Join Date: Mar 2005 Location: Scottsdale, Arizona Posts: 98	Fan Speed When I run my fan for my A/C I can not get the high speed to run. Any ideas? New switch and fan have been installed. Thanks. __________________ 1972 Chevy Cheyenne 20 1979 Chevy Camaro 2007 Chevy Avalanche 2005 Mini Cooper

06-07-2006, 08:20 PM	#2
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,728	Re: Fan Speed I think there's a relay (under the dash?) that operates on the high-speed fan setting... __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

06-07-2006, 09:34 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Fan Speed Yup, on A/C trucks there is a relay.

06-08-2006, 10:19 AM	#4
ssjones Registered User Join Date: Mar 2005 Location: Scottsdale, Arizona Posts: 98	Re: Fan Speed Anyone possibly have a pic to know what I am looking for. Is this near the fuse panel? Thanks. __________________ 1972 Chevy Cheyenne 20 1979 Chevy Camaro 2007 Chevy Avalanche 2005 Mini Cooper

06-08-2006, 10:21 AM	#5
blazerparts No,I DON'T have Tourett's Join Date: Mar 2005 Location: Reno, NV Posts: 556	Re: Fan Speed I think it should be on the firewall under the glovebox. __________________ '72 K5 CST 350/350 Daily Driver '69 GMC3500 Camper Special CST Flatbed 396/400 Upgraded to show truck '69 GMC 2500 L6292, 3spd beater

06-08-2006, 10:37 PM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Fan Speed yeah, it is on the passenger side somewhere. I can't remember where though, it looks just like the metal one by the fuse box, but that one is for the horn.

06-10-2006, 03:30 PM	#7
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,728	Re: Fan Speed I am an idiot-- I don't understand anything computer related. I have a digital pic of the relay, it's in my computer, and I can view it in HP Image Zone -- but I have no clue how to get it to Photobucket so I can (maybe) show it here. Sigh... It's behind the dash, to the right of the heater controls, near the lighter. Mine was just floating loose, possibly b/c it got in the way when fiddling with A/C ducting while replacing the glovebox many years ago. It has a black cover, measures ~1' x 2", and is ~1 1/2" tall. The bracket has a black (ground?) wire attached. There are two electrical connectors -- a single with an orange wire, and a triple with blue, purple, and yellow wires. I hope this helps -- sorry about no pic! __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

06-10-2006, 08:22 PM	#8
stope4 Registered User Join Date: Jan 2006 Location: Houston Posts: 434	Re: Fan Speed On 71 and 72s there are two relays. One is attached to bottom of dash to right of ac controls. This is the antidieseling relay. (not really sure what it's for) The second relay is attached to under dash ac box on passenger side. This is the ac fan relay. It is between the passenger kick panel and the ac box. You may have to take glove box out to see it. There are four electrical connectors on the relay. Two wiring harness connectors attach to these. One of the connectors has three wirs and one connector has one. The wire connector going to the one prong is the high speed relay. Your problem may be as simple as this connector needing to be attached. I believe 67 - 70 has only the ac blower relay and it's similar to the one for 71 and 72 but may be attached somewhere else.

06-11-2006, 12:46 AM	#10
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Fan Speed You can see it by looking up between the glove box and kick panel. this relay MUST be grounded. Take a jumper wire with clips and contect one end to relay and the other to ground. If your high speed works you have found your problem. ( there is a small black wire that is supposed to be attached to the one of the screws that mounts the relay to the ac box--if there is one there check to see if it is tight as these screws strip easy) If still does not work trace the large red (sometimes orange) wire back to the fuse panel to see if it is plugged in. This plug in gets loose and will heat up over time and corrode enough that it will loose connection. (check next post) __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

06-11-2006, 12:56 AM	#11
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Fan Speed here is where it will plug in: this wire feeds high speed only--rest of speeds get the current through switch. (you can check your fan motor for high speed by removing wire from blower motor and run a jumper from motor to plus post on battery) Attached Images __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

06-11-2006, 01:16 AM	#12
Richard Senior Member Join Date: Dec 1999 Location: Southern California Posts: 2,896	Re: Fan Speed It has been a while since I looked at the wiring. I might be able to look it up later for you. One thing that comes to mind is how the fan speeds hook up. There is a resistor that is mounted in the air duct that actually controls the fans speed that has power going to it, but if I remember correctly the high fan speed has a straight wire that runs all the way back to the fuse panel. The reason this comes to mind is that wire was all hacked and not hooked up in my truck. after re-reading looks like I was beat on my explaination. __________________ Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746

06-12-2006, 07:11 PM	#13
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,728	Re: Fan Speed I know this is a bit late, but with help from my daughter, here's a pic of the relay __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay



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