Power to A/C compressor - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Raindoc · 09-19-2008, 09:04 PM

Just bought a 72 Blazer w/a/c. I had one 27 years ago when I was in college. I am trying to work out some wiring issues,#1 getting the air to operate. Question: can someone walk me through the switch(s), relays,sensors etc that carry power from the controls omn the dash to the compressor clutch? Mine had an aftermarket switch that sent power to the compressor but I want it like it should be. What postion on the control panel activates the compressor? I can not identify a switch unless the fan switch has a position that does it. One of the wires leaving the fan switch activates a relay located under the glove box but my fan switch is bad so I cannot test it-yet. Does that relay control the compressor? Also is there a good wiring diagram for 72 Blazer available? Thanks and I really apriciate this forum.

Critter · 09-19-2008, 09:15 PM

This will probably be a good start for you.

http://67-72chevytrucks.com/vboard/s...ghlight=wiring

Just realized this doesn't have much as far as A/C wiring, but it shows the heater fan and relay circuit.

JimKshortstep4x4 · 09-20-2008, 05:36 AM

Here is a picture of the AC wiring diagram.

Jim

LUV2XCLR8 · 09-20-2008, 05:48 AM

If it's all OE Wiring maybe it's time to upgrade? M&H has a
wiring set-up just like factory with all of the factory ends.

Raindoc · 09-20-2008, 09:23 AM

Thanks guys. The diagram helps but there are some differences between it and my blazer's wiring. My fan switch seems to only have a high & low fan speed (again it is not working at all but I can only find three positions). I only have three wires in the plug; one from fuse box, one to fan relay, one for high and one for low. Was there another switch used or is mine so far gone that it does not show up. Is the compressor switch/diverter cable located on the back of the lower air box on the fire wall side just above the passinger's left foot? Where is the "diebeling relay" located? Where is the fan resistor located.

What is the benefit in upgrading the wiring? Mine looks good in general. although the wire to the compressor has been cut at the fan and there may be a wire missing for the fan switch.

JimKshortstep4x4 · 09-20-2008, 07:16 PM

I don't know about your switch as the originals had (4) wires, (one power, three for speeds).The compressor switch and diverter cable are located on the diverter box
which is the box just right of the "S" connector.

The anti diesel relay was used on trucks that were equipped with an idle solenoid. Your harness may not be wired with the connector for the relay. The AC will work fine without the relay.

The fan resistor is located inside the heater box, (box to the far right). If you remove the diverter box, you can see it.

Jim

09-19-2008, 09:15 PM	#2
Critter Future TOTM Winner Join Date: Aug 2006 Location: Bulverde, TX Posts: 2,692	Re: Power to A/C compressor This will probably be a good start for you. http://67-72chevytrucks.com/vboard/s...ghlight=wiring Just realized this doesn't have much as far as A/C wiring, but it shows the heater fan and relay circuit. __________________ 72 Chevy CST K5 HIGHLANDER BLAZER Getting a 6.0,NV4500,NP205,14BFF (Currently laying all over the place in little pieces) 72 Chevy swb step-side "LS" 6.0 Here's a build thread of sorts 2002 HD2500 Crew Cab, 8.1L Allison 4x4 Daily Driver Check it out www.lsdyno.com Last edited by Critter; 09-19-2008 at 09:19 PM.

09-20-2008, 05:36 AM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: Power to A/C compressor Here is a picture of the AC wiring diagram. Jim Attached Images __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

09-20-2008, 05:48 AM	#4
LUV2XCLR8 The LuvShack Garage Join Date: Jan 2004 Location: Maple Grove, TN (West Side) Posts: 30,470	Re: Power to A/C compressor If it's all OE Wiring maybe it's time to upgrade? M&H has a wiring set-up just like factory with all of the factory ends. __________________ Owner/Op: "TN Classic Transport Carriers" The Toy: "Square Vette" 72 Hybrid Blazer Toy Barn: "LuvShack" 40 x 60 x 20 Shop Big Piggy: "Goliath" 07 Kodiak C4500 Lil Piggy:"Maddy" 88 Silverado 3500 Hauler: "Feathers" 14 Aluma 8218T

09-20-2008, 09:23 AM	#5
Raindoc Registered User Join Date: Sep 2008 Location: Garner North Carolina Posts: 24	Re: Power to A/C compressor Thanks guys. The diagram helps but there are some differences between it and my blazer's wiring. My fan switch seems to only have a high & low fan speed (again it is not working at all but I can only find three positions). I only have three wires in the plug; one from fuse box, one to fan relay, one for high and one for low. Was there another switch used or is mine so far gone that it does not show up. Is the compressor switch/diverter cable located on the back of the lower air box on the fire wall side just above the passinger's left foot? Where is the "diebeling relay" located? Where is the fan resistor located. What is the benefit in upgrading the wiring? Mine looks good in general. although the wire to the compressor has been cut at the fan and there may be a wire missing for the fan switch.

09-20-2008, 07:16 PM	#6
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: Power to A/C compressor I don't know about your switch as the originals had (4) wires, (one power, three for speeds).The compressor switch and diverter cable are located on the diverter box which is the box just right of the "S" connector. The anti diesel relay was used on trucks that were equipped with an idle solenoid. Your harness may not be wired with the connector for the relay. The AC will work fine without the relay. The fan resistor is located inside the heater box, (box to the far right). If you remove the diverter box, you can see it. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

09-19-2008, 09:04 PM	#1
Raindoc Registered User Join Date: Sep 2008 Location: Garner North Carolina Posts: 24	Power to A/C compressor Just bought a 72 Blazer w/a/c. I had one 27 years ago when I was in college. I am trying to work out some wiring issues,#1 getting the air to operate. Question: can someone walk me through the switch(s), relays,sensors etc that carry power from the controls omn the dash to the compressor clutch? Mine had an aftermarket switch that sent power to the compressor but I want it like it should be. What postion on the control panel activates the compressor? I can not identify a switch unless the fan switch has a position that does it. One of the wires leaving the fan switch activates a relay located under the glove box but my fan switch is bad so I cannot test it-yet. Does that relay control the compressor? Also is there a good wiring diagram for 72 Blazer available? Thanks and I really apriciate this forum.



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