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Discussion Starter · #1 ·
I'm to the point of putting the wiring back in the car and pulled out my harnesses that I've been collecting. I noticed two different heater circuit harnesses. One has two relay looking plug-ins that were screwed to the inside dash mounting bracket. This harness came out of a '71 AC car. Another harness I have (which is in better condition) does not have these two relays. They both have the blower realy under the hood.
I couldn't locate this part of the circuit in the assembly manual schematics.
Does any one know what these two relays are for?? If I don't need them I could use the other harness.
I've installed an AC delete box.

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Doug, Chevl71
TC #625, GACClub CM028, ACES 05023
(OO ss OO)
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John Muha is our resident '71 export (among many other years), but I'll stab at this. These relays (or at least one of them) cause the AC compressor to remain engaged for a couple seconds when you switch the engine off to prevent run-on. My car doesn't have the compressor (looking for one plus hoses), but it does have these relays, and the fan continues to blow for about two seconds whenever I turn the key off.

BTW, the '71 were wired for heaters, if A/C was added the heater harness was tied up and replaced with an A/C harness. You'll have two sets of heater wiring inside, and may find the second orange heater blower wire under your hood.

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Cecil Hawkins
San Diego, CA
1971 GMC Sprint
The Project
All I need is time...and some $$$
"Tourist, go home! And take someone with you!"
 

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Actually Elree Colby does a far better job on harnesses than I. The two relays are the blocking relay and the anti-dieseling relay. These were used on the 71 A/C harness that you have. Since you don't know what the "other A/C" harness is, watch out for it. If it is a Chevelle harness, the 72s look real close. However, they use different pins in the firewall connector.
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by chevl71:
I couldn't locate this part of the circuit in the assembly manual schematics.
<HR></BLOCKQUOTE>

Do you have the full assembly manual or did you get them separate? I ordered just the wiring diagram, and it turns out I wasted the $$$. There are two or three versions of the same diagrams in the full manual, and the A/C wiring is in another section of the manual completely.

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Cecil Hawkins
San Diego, CA
1971 GMC Sprint
The Project
All I need is time...and some $$$
"Tourist, go home! And take someone with you!"
 

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Discussion Starter · #5 ·
I bought the reprint assembly manual that has wiring diagrams in it. Didn't spend a lot of time trying to find what I wanted. The harnesses I kept/have would be 71-72 Chevelle, so thanks for the tip on the pin-out differences. I think I'll keep the harness with the relays in the car and repair/wrap the area that needs attention (I bought the non-sticky correct wrap). The blower relay connector needs a little attention.
Thanks guys for the guidance!

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Doug, Chevl71
TC #625, GACClub CM028, ACES 05023
(OO ss OO)
chevl71 homepage
 

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chevl71, the '71 harness is the only year which used the two relays under the dash as you describe them. You can see the wiring routing in the C60 option section (A/C) of the factory assembly manual for 1971. Elree Colby clued me in to the fact that these relays are '71 only. I traced every single wire in the harness and determined that the relays are not necessary even if you were repairing the original A/C system to operate normally. You can remove all the wiring of the relays which includes a long pink wire that piggybacks into the IGN term of the fuse panel and you only need to clip the brown wire that shares a connector on the master blower switch that is operated by the upper A/C mode lever. The rest of the wiring operates only the A/C compressor clutch or the speed of the blower motor.
Can be a little confusing at first but if you take your time and trace the circuits, you'll be able to see what goes where.

Good luck,

Louie Hammel
 
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