Need A/C relay help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mstacy · 04-01-2002, 06:44 PM

The service manual shows an anti-dieseling relay that should be plugged into the a/c wiring harness under the dash. This is not the one over by the glove box/ right kick panel area. This one plugs in around the center controls, behind the dash. Does anyone have one of these or know the GM part number? I can't seem to find any and the blower won't work without it. The circuit isn't complete I guess. Thanks!

------------------
Mike Stacy, S. Calif.
1971 Factory Hugger Orange Shortbed, 350/350, 20" Torq Thrusts, 3/5 drop (belongs to my son Christopher now) I am looking for a rustfree loaded 71-72 Burb.

71Chev · 04-01-2002, 06:56 PM

Sounds like your high speed fan relay or fan switch is shot.
I have my anti-dieseling relay unhooked and my blower works fine.
Have you checked the relay inside the heater box?
------------------

71 Chevy CST Long Fleet 350/350/3.07 leaf rear.
Email: 67-72truckparts@nanosecond.com

[This message has been edited by 71Chev (edited April 01, 2002).]

71Chev · 04-01-2002, 07:14 PM

To check the relay inside the plenum there is a small vent on the bottom of the box near passengers left foot in the cab. Pull it open or if already open squeeze the sides so the small vent pops out. Look up in that square hole, you'll see the relay. It has a smaller coil and a larger coil. If one is burnt you'll be able to tell.

------------------

71 Chevy CST Long Fleet 350/350/3.07 leaf rear.
Email: 67-72truckparts@nanosecond.com

mstacy · 04-01-2002, 11:21 PM

Everything is pretty much new. The wiring harness is a new replacement from Brother's. I did use a jumper on the 3 prong pigtail where I think the anti-diesel relay plugs into and the fan worked. That makes me think something needs to plug into the pigtail, like a relay or something in order to work. Any suggestions are appreciated.

Hutch · 04-02-2002, 12:10 AM

I just went over my whole factory a/c system.
Where is the pigtale you are referring to located?
What color are the wires?
You did say that the highspeed relay by the kick panel is good.

------------------
John Hutchison
Grapevine,Texas
76051
71 1/2 ton swb 307 pg
69 Jaguar XK-E 4.2 Roadster

Hutch · 04-02-2002, 12:35 AM

The one I have is a Delco Remy 811-12V and mounts under the dash between the radio and glove box and grounds to the lower lip of the dash. It has three prongs,
The description in LMC's catalog list it as Relay a/c Blower $14.95

------------------
John Hutchison
Grapevine,Texas
76051
71 1/2 ton swb 307 pg
69 Jaguar XK-E 4.2 Roadster

mstacy · 04-02-2002, 01:16 AM

Hutch, that's the one. I guess it's the high blower relay then and not anti-dieseling. I guess that makes sense why it doesn't work!! It's alway the simple things that gets ya. Thanks for your help. I see the relay in LMC.

71Chev · 04-02-2002, 08:56 AM

That relay Hutch is talking about is the one I have unhooked. My fan wouldn't run on High just on low and med. Until I unpluged that relay, I guess since the anit-dieseling relayisn't hooked up under the hood. My harnesses are uncut original. The anti diesleling relay is mounted to the bottom lip of the dash. Number 16 in LMC has four prongs, and is the highspeed fan relay that mounts near the pass. fresh air vent on the plenum. The other relay is inside the plenum.

------------------

71 Chevy CST Long Fleet 350/350/3.07 leaf rear.
Email: 67-72truckparts@nanosecond.com

mstacy · 04-02-2002, 10:15 AM

THe one in LMC #16 has 4 prongs doesn't it. My pigtail only has 3. I don't have any other relays other than the ones already mentioned. The one is LMC looks more like the one over on the passenger side by the plenum. I don't have one under the hood that I can remember. Where is your located?

The other one located inside the A/C box in the interior, is actually a resistor. That's the one with the wire coils. That also looks good.

When I jumper the pongs on the anti-diesel relay, the blower works which leads me to think that is the problem. Now I am lost! Any ideas?

71Chev · 04-02-2002, 10:53 AM

That's the high speed fan relay you see in the LMC catalog and yes it does have 4 prongs.

My fan works great now that I unplugged the anti-dieseling realy. (one on the dash lip)

I'm stumped. Have you tried bypassing the high speed relay with jumper wires in the plug? with and w/o the dieseling relay hooked up?
I guess I'd replace the high speed fan relay. You might be able to get it at your local parts house.

------------------

71 Chevy CST Long Fleet 350/350/3.07 leaf rear.
Email: 67-72truckparts@nanosecond.com

[This message has been edited by 71Chev (edited April 02, 2002).]

Hutch · 04-02-2002, 12:40 PM

When my high speed fan relay was on the fritz(broken ground wire) the symptons were:
when the three speed switch on the a/c control was on low and medium it worked ok but switch to high it would go back to low.
I was troubleshooting the circuit when I accidentaly grounded the case of the relay. With the fan switch being in the high
position the blower increased substantualy in rpm's
Pay special attention to your ground leads. The high speed relay on near the kick panel has a black lead whick is attached to the firewall and the one on the dash lip is grounded through a screw to the case of the relay.

mstacy · 04-02-2002, 01:06 PM

My truck didn't have A/C originally, I added it a piece at a time using mostly new or NOS pieces. I don't remember seeing a black ground wire for the relay. The new harness had wires for all prongs of the relay but no seperate black ground wire. I used 2 screws and secured it to the firewall area which should be a good ground anyway. This has got me miffed.

mstacy · 04-02-2002, 06:09 PM

71 Chev and Hutch....THANKS!! It was the relay afterall. I replaced it with another one and it works great. I tried that the other day and got nothing, so I am not sure what really fixed what, but it works and that's all that matters.

71Chev · 04-02-2002, 06:13 PM

Good deal!

------------------

71 Chevy CST Long Fleet 350/350/3.07 leaf rear.
Email: 67-72truckparts@nanosecond.com

04-01-2002, 06:56 PM	#2
71Chev Senior Member Join Date: Dec 2000 Location: Indiana Posts: 3,074	Sounds like your high speed fan relay or fan switch is shot. I have my anti-dieseling relay unhooked and my blower works fine. Have you checked the relay inside the heater box? ------------------ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear. Email: 67-72truckparts@nanosecond.com [This message has been edited by 71Chev (edited April 01, 2002).] __________________ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear.

04-01-2002, 07:14 PM	#3
71Chev Senior Member Join Date: Dec 2000 Location: Indiana Posts: 3,074	To check the relay inside the plenum there is a small vent on the bottom of the box near passengers left foot in the cab. Pull it open or if already open squeeze the sides so the small vent pops out. Look up in that square hole, you'll see the relay. It has a smaller coil and a larger coil. If one is burnt you'll be able to tell. ------------------ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear. Email: 67-72truckparts@nanosecond.com __________________ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear.

04-01-2002, 11:21 PM	#4
mstacy Senior Member Join Date: May 2000 Location: Upland, CA 91784 (Los Angeles) Posts: 191	Everything is pretty much new. The wiring harness is a new replacement from Brother's. I did use a jumper on the 3 prong pigtail where I think the anti-diesel relay plugs into and the fan worked. That makes me think something needs to plug into the pigtail, like a relay or something in order to work. Any suggestions are appreciated. __________________ Mike Stacy, S. Calif. 1971 Factory Hugger Orange Shortbed, 350/350, 20" Torq Thrusts, 3/5 drop (belongs to my son Christopher now)

04-02-2002, 12:10 AM	#5
Hutch Registered User Join Date: Oct 2001 Location: Grapevine, Tx. Posts: 2,142	I just went over my whole factory a/c system. Where is the pigtale you are referring to located? What color are the wires? You did say that the highspeed relay by the kick panel is good. ------------------ John Hutchison Grapevine,Texas 76051 71 1/2 ton swb 307 pg 69 Jaguar XK-E 4.2 Roadster __________________ John Hutchison Grapevine,Texas 68 1/2 t swb 68 Mustang 69 Jaguar 71 1/2 t swb 88 Supra CompTs6m 93 Escort GT 2005 Corolla XRS

04-02-2002, 12:35 AM	#6
Hutch Registered User Join Date: Oct 2001 Location: Grapevine, Tx. Posts: 2,142	The one I have is a Delco Remy 811-12V and mounts under the dash between the radio and glove box and grounds to the lower lip of the dash. It has three prongs, The description in LMC's catalog list it as Relay a/c Blower $14.95 ------------------ John Hutchison Grapevine,Texas 76051 71 1/2 ton swb 307 pg 69 Jaguar XK-E 4.2 Roadster __________________ John Hutchison Grapevine,Texas 68 1/2 t swb 68 Mustang 69 Jaguar 71 1/2 t swb 88 Supra CompTs6m 93 Escort GT 2005 Corolla XRS

04-01-2002, 06:44 PM	#1
mstacy Senior Member Join Date: May 2000 Location: Upland, CA 91784 (Los Angeles) Posts: 191	Need A/C relay help The service manual shows an anti-dieseling relay that should be plugged into the a/c wiring harness under the dash. This is not the one over by the glove box/ right kick panel area. This one plugs in around the center controls, behind the dash. Does anyone have one of these or know the GM part number? I can't seem to find any and the blower won't work without it. The circuit isn't complete I guess. Thanks! ------------------ Mike Stacy, S. Calif. 1971 Factory Hugger Orange Shortbed, 350/350, 20" Torq Thrusts, 3/5 drop (belongs to my son Christopher now) I am looking for a rustfree loaded 71-72 Burb. __________________ Mike Stacy, S. Calif. 1971 Factory Hugger Orange Shortbed, 350/350, 20" Torq Thrusts, 3/5 drop (belongs to my son Christopher now)

04-02-2002, 01:16 AM	#7
mstacy Senior Member Join Date: May 2000 Location: Upland, CA 91784 (Los Angeles) Posts: 191	Hutch, that's the one. I guess it's the high blower relay then and not anti-dieseling. I guess that makes sense why it doesn't work!! It's alway the simple things that gets ya. Thanks for your help. I see the relay in LMC. __________________ Mike Stacy, S. Calif. 1971 Factory Hugger Orange Shortbed, 350/350, 20" Torq Thrusts, 3/5 drop (belongs to my son Christopher now)

04-02-2002, 08:56 AM	#8
71Chev Senior Member Join Date: Dec 2000 Location: Indiana Posts: 3,074	That relay Hutch is talking about is the one I have unhooked. My fan wouldn't run on High just on low and med. Until I unpluged that relay, I guess since the anit-dieseling relayisn't hooked up under the hood. My harnesses are uncut original. The anti diesleling relay is mounted to the bottom lip of the dash. Number 16 in LMC has four prongs, and is the highspeed fan relay that mounts near the pass. fresh air vent on the plenum. The other relay is inside the plenum. ------------------ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear. Email: 67-72truckparts@nanosecond.com __________________ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear.

04-02-2002, 10:15 AM	#9
mstacy Senior Member Join Date: May 2000 Location: Upland, CA 91784 (Los Angeles) Posts: 191	THe one in LMC #16 has 4 prongs doesn't it. My pigtail only has 3. I don't have any other relays other than the ones already mentioned. The one is LMC looks more like the one over on the passenger side by the plenum. I don't have one under the hood that I can remember. Where is your located? The other one located inside the A/C box in the interior, is actually a resistor. That's the one with the wire coils. That also looks good. When I jumper the pongs on the anti-diesel relay, the blower works which leads me to think that is the problem. Now I am lost! Any ideas? __________________ Mike Stacy, S. Calif. 1971 Factory Hugger Orange Shortbed, 350/350, 20" Torq Thrusts, 3/5 drop (belongs to my son Christopher now)

04-02-2002, 10:53 AM	#10
71Chev Senior Member Join Date: Dec 2000 Location: Indiana Posts: 3,074	That's the high speed fan relay you see in the LMC catalog and yes it does have 4 prongs. My fan works great now that I unplugged the anti-dieseling realy. (one on the dash lip) I'm stumped. Have you tried bypassing the high speed relay with jumper wires in the plug? with and w/o the dieseling relay hooked up? I guess I'd replace the high speed fan relay. You might be able to get it at your local parts house. ------------------ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear. Email: 67-72truckparts@nanosecond.com [This message has been edited by 71Chev (edited April 02, 2002).] __________________ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear.

04-02-2002, 12:40 PM	#11
Hutch Registered User Join Date: Oct 2001 Location: Grapevine, Tx. Posts: 2,142	When my high speed fan relay was on the fritz(broken ground wire) the symptons were: when the three speed switch on the a/c control was on low and medium it worked ok but switch to high it would go back to low. I was troubleshooting the circuit when I accidentaly grounded the case of the relay. With the fan switch being in the high position the blower increased substantualy in rpm's Pay special attention to your ground leads. The high speed relay on near the kick panel has a black lead whick is attached to the firewall and the one on the dash lip is grounded through a screw to the case of the relay. __________________ John Hutchison Grapevine,Texas 68 1/2 t swb 68 Mustang 69 Jaguar 71 1/2 t swb 88 Supra CompTs6m 93 Escort GT 2005 Corolla XRS

04-02-2002, 01:06 PM	#12
mstacy Senior Member Join Date: May 2000 Location: Upland, CA 91784 (Los Angeles) Posts: 191	My truck didn't have A/C originally, I added it a piece at a time using mostly new or NOS pieces. I don't remember seeing a black ground wire for the relay. The new harness had wires for all prongs of the relay but no seperate black ground wire. I used 2 screws and secured it to the firewall area which should be a good ground anyway. This has got me miffed. __________________ Mike Stacy, S. Calif. 1971 Factory Hugger Orange Shortbed, 350/350, 20" Torq Thrusts, 3/5 drop (belongs to my son Christopher now)

04-02-2002, 06:09 PM	#13
mstacy Senior Member Join Date: May 2000 Location: Upland, CA 91784 (Los Angeles) Posts: 191	71 Chev and Hutch....THANKS!! It was the relay afterall. I replaced it with another one and it works great. I tried that the other day and got nothing, so I am not sure what really fixed what, but it works and that's all that matters. __________________ Mike Stacy, S. Calif. 1971 Factory Hugger Orange Shortbed, 350/350, 20" Torq Thrusts, 3/5 drop (belongs to my son Christopher now)

04-02-2002, 06:13 PM	#14
71Chev Senior Member Join Date: Dec 2000 Location: Indiana Posts: 3,074	Good deal! ------------------ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear. Email: 67-72truckparts@nanosecond.com __________________ 71 Chevy CST Long Fleet 350/350/3.07 leaf rear.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.