A.C. Blower question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**landarts** · 07-02-2009, 03:24 PM

First let me give you a little background. The truck is a 72 lwb Cheyenne with factory air, that I am in the process of restoring. When I purchased the truck several years ago the hot and cold lever on the A.C. controls was broken and the fan switch would only do low and medium-- no high setting. I removed the switch and sanded the contacts and applied die-electric grease to contact points. Still no High setting. One more thing the heater core was toast . So I replaced the heater core, rebuilt the A.C. control unit with new levers, and replaced the fan switch.

When I turn the key to ACC and put the switch in high mode it blows like crazy. When the truck is running I dont get half of air in high mode versus when the motor is not running. My questions is does the A.C. relay have anything to do with that or am I just fishin....?

thanks
Jim

Longhorn Man · 07-02-2009, 03:31 PM

I would double check the ground on the relay... then start inspecting the wires to the relay and see whats up.

**landarts** · 07-02-2009, 05:49 PM

I grounded the relay to the firewall and I double checked it. Is there any way to test a A.C. relay or do you just buy another ?

Longhorn Man · 07-02-2009, 07:59 PM

if it kicks on when the key is in the Acc position, then it is good.

**leddzepp** · 07-02-2009, 09:45 PM

If it is spinning faster in the ACC position than it is when in the ON position, something is wrong. The fan should spin at the same speed regardless of the position of the key. I had this problem a while back, and when the fan spun too fast, I could smell burning after a while. I replaced my relay and the problem was solved. I do not know if that will solve your problem, but I think it is worth $10 to find out if nothing else is solving the problem.

**landarts** · 07-03-2009, 08:51 PM

Hey thanks for the input , I will try a new relay switch an report back what I find.

thanks again
Jim

**WorkinLonghorn** · 07-03-2009, 09:03 PM

I think what LHM says is correct; If it runs correctly on ACC then the relay must be good. I don't know how those things are wired,but obviously there are two circuits and the one that "Run" activates is faulty.

**leddzepp** · 07-04-2009, 02:35 AM

If I am reading this correctly, you are saying that the fan motor spins faster when the key is in the ACC position, than it does when the engine is running or in the ON position. Or are you just talking about an overall loss of air volume being put out? If that is the case, then the problem is not the relay. Check the kick panel (recirc) door on the pass side. It should be open when the A/C is on, truck running. The fresh air door, underneath the cowling on the outside pass. side should be closed.

**landarts** · 07-04-2009, 07:31 AM

I will check that out today before I buy a new relay. I will report back what I find.

07-02-2009, 03:24 PM	#1
landarts landarts Join Date: May 2005 Location: Star, Idaho Posts: 1,354	A.C. Blower question First let me give you a little background. The truck is a 72 lwb Cheyenne with factory air, that I am in the process of restoring. When I purchased the truck several years ago the hot and cold lever on the A.C. controls was broken and the fan switch would only do low and medium-- no high setting. I removed the switch and sanded the contacts and applied die-electric grease to contact points. Still no High setting. One more thing the heater core was toast . So I replaced the heater core, rebuilt the A.C. control unit with new levers, and replaced the fan switch. When I turn the key to ACC and put the switch in high mode it blows like crazy. When the truck is running I dont get half of air in high mode versus when the motor is not running. My questions is does the A.C. relay have anything to do with that or am I just fishin....? thanks Jim

07-02-2009, 03:31 PM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: A.C. Blower question I would double check the ground on the relay... then start inspecting the wires to the relay and see whats up.

07-02-2009, 05:49 PM	#3
landarts landarts Join Date: May 2005 Location: Star, Idaho Posts: 1,354	Re: A.C. Blower question I grounded the relay to the firewall and I double checked it. Is there any way to test a A.C. relay or do you just buy another ?

07-02-2009, 07:59 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: A.C. Blower question if it kicks on when the key is in the Acc position, then it is good.

07-02-2009, 09:45 PM	#5
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 19,996	Re: A.C. Blower question If it is spinning faster in the ACC position than it is when in the ON position, something is wrong. The fan should spin at the same speed regardless of the position of the key. I had this problem a while back, and when the fan spun too fast, I could smell burning after a while. I replaced my relay and the problem was solved. I do not know if that will solve your problem, but I think it is worth $10 to find out if nothing else is solving the problem. __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man

07-03-2009, 08:51 PM	#6
landarts landarts Join Date: May 2005 Location: Star, Idaho Posts: 1,354	Re: A.C. Blower question Hey thanks for the input , I will try a new relay switch an report back what I find. thanks again Jim

07-03-2009, 09:03 PM	#7
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,861	Re: A.C. Blower question I think what LHM says is correct; If it runs correctly on ACC then the relay must be good. I don't know how those things are wired,but obviously there are two circuits and the one that "Run" activates is faulty. __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, 2nd owner, Work-Truck supreme. Best $300 I ever spent.

07-04-2009, 02:35 AM	#8
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 19,996	Re: A.C. Blower question If I am reading this correctly, you are saying that the fan motor spins faster when the key is in the ACC position, than it does when the engine is running or in the ON position. Or are you just talking about an overall loss of air volume being put out? If that is the case, then the problem is not the relay. Check the kick panel (recirc) door on the pass side. It should be open when the A/C is on, truck running. The fresh air door, underneath the cowling on the outside pass. side should be closed. Last edited by leddzepp; 07-04-2009 at 02:37 AM.

07-04-2009, 07:31 AM	#9
landarts landarts Join Date: May 2005 Location: Star, Idaho Posts: 1,354	Re: A.C. Blower question I will check that out today before I buy a new relay. I will report back what I find.



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