Bypassing 71 anti diesel & blocking relays - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 8 (permalink) Old Oct 5th, 19, 5:27 PM Thread Starter
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Bypassing 71 anti diesel & blocking relays

I have been reading old posts about my 1971 el camino A/C anti-dieseling relay and blocking relay. I have found companies that are throwing away relays because of age due to returns f/ warranty (didn't know anyone allowed electric part returns) the only thing I see that could go wrong is the points in relay being corroded from age and an emery board would clean that up. I have an AAW a/c harness in elky and AAW only tells you you have to have everything hooked up (including relays) for system to work properly. Yet I have read a number of posts that say you can do w/o them. One man saids jump the tan and lt blue wire on anti dieseling relay (thats what picture shows) another saids you only need blocking relay. Since this is a One Year Only set-up Chevrolet has come up w/ a easier solution and got rid of these relays after one year.
SO THE QUESTION IS; CAN YOU JUMP RELAYS or HOW DO YOU BYPASS THEM AND STILL HAVE YOUR COMRESSOR COME ON WHEN TURNED ON.
I just want to know positively and from experiance how to eliminate / bypass relays?
Tony
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post #2 of 8 (permalink) Old Oct 5th, 19, 6:43 PM
Art
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Re: Bypassing 71 anti diesel & blocking relays

When I rebuilt the dash this summer I lost the blocking relay. Once the dash was back in the car I was running electrical test on all the systems and when I got to the air conditioning the compressor clutch wouldn't energize. I looked every where for the relay and tried to find one with the reproduction vendors but didn't find it. I removed the anti-dieseling relay and put it in spare parts box, then jumped the tan and light blue wires as you said to get the clutch to engage. That got every thing working but no anti-dieseling function. I didn't need it since my 71 is now has EFI. by the way, I charged the air conditioning with Freon this afternoon.
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post #3 of 8 (permalink) Old Oct 5th, 19, 7:42 PM Thread Starter
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Re: Bypassing 71 anti diesel & blocking relays

Thanks Art, Finally a no B.S. Answer. Just jump the tan and Lt. blue wires that normally would go to Anti-Dieseling relay and disconnect the blocking relay. Now what happens w/ pink wire from Blocking relay that is plugged into Ignition Terminal on Fuse panel?
one of my problems I had w/ no power to comp was I had a three wire plug left over in back of A/C - Heater control. I found out by searching ebay that the comp switch was missing from back of my unit. From front you would see two spades sticking up that connected to switch at back . I ordered a complete reman unit f/ a guy in Florida. so once relays are eliminated I can check and proceed to button this dash up once and forever.
Tony
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post #4 of 8 (permalink) Old Oct 5th, 19, 9:36 PM
Art
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Re: Bypassing 71 anti diesel & blocking relays

You can leave the pink wire if you want to, I did, but according to the wiring diagram when the ignition is turned off the pink wire triggers the anti-dieseling system. The blocking relay disconnects the compressor from the rest of the cars electrical system and the anti-dieseling relay is a time delay that turns the compressor on for a short time. The idea was to add some load to the engine so it wouldn't diesel. The compressor has to be isolated by the blocking relay or the anti-dieseling relay would "back feed" power to the ignition system and the car would keep running.

Just so you know, every time I've buttoned up my dash "forever", that only lasted a few months at most. I'm always coming up with dumb ideas for the Chevelle which requires digging into it again.
71350SS and hydro462 like this.
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post #5 of 8 (permalink) Old Oct 6th, 19, 12:33 PM Thread Starter
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Re: Bypassing 71 anti diesel & blocking relays

I spoke TOO SOON- My brand new Quartz clock that basically uses no pwr began making no noise like bad gear- then My turn signal arrows quit lighting up when you flip on either side. The turn signals work outside and flashers work. I tried changing bulbs and cleaning contacts but still no little green arrows. Just like the album "GHOST IN THE MACHINE" I think this elky is haunted. I could see if I was making custom modification but it is stock. Stock SS dash (original) and I especially made sure dash was grounded good in a number of spots like,chassis,body and motor. I am thinking of changing out circuit board. I got this white thing in there and I remember the factory one was green but who knows what taiwanese company is making this crap. I sure hope Trump straightens out trade and gets more companys back here making stuff. Restoring a vehicle today is a real pain.
As far as pink wire if I disconnect the two relays I'll disconnect pink wire. I am afraid to have a hot wire just dangling under dash. Thanks Art
Tony
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post #6 of 8 (permalink) Old Oct 6th, 19, 1:36 PM Thread Starter
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Re: Bypassing 71 anti diesel & blocking relays

HEY ART, I OWE YOU BIG TIME BROTHER!!! I jumped 2 wire plug for switch I am missing on ac/heater control unit and ran a jumper to Anti-Dieseling Relay wires Lt. Blue & Tan and disconnected BOTH RELAYS and I HAVE POWER AT COMPRESSOR. Now Once I get Reman Unit and install it I will not have any more problems w/ A/C comp Power. This is a big one off list. Your better than guy f/ AAW who I was on phone with for over an hour and complaining about this problem with for 8 months. 1 post and done. should be a new saying. Too bad I am gonna miss the 60 Annv El Camino celebration this week in Arlington , Texas. My reservations back in January and still not done BUT got a big headache off list.
Thanks very much.
Tony
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post #7 of 8 (permalink) Old Oct 6th, 19, 11:00 PM
Art
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Re: Bypassing 71 anti diesel & blocking relays

My pleasure Tony.

Your turn signal reminds me of one I had right after I bought the car. The turn signal indicators wouldn't work unless you turned on the head lights then they both flashed. When you have weird electrical problems like that it's nearly always a ground. In this case it was a screw that held the plastic circuit board on the back of the gauge cluster made up the ground for those bulbs that was loose.

When I rebuilt the dash this summer I bought a new circuit board and it seems to work fine so far. Check your ground screws and connector plugs. If I remember right, there are two plugs, a rectangle one on the back of the gauge cluster and a harmonica looking connector on the column. Make sure all the contacts and grounds are clean and tight. If that's not it, it'll be time to break out the volt meter and wiring diagram and start tracing from the turn signal switch to the gauge cluster.
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post #8 of 8 (permalink) Old Oct 7th, 19, 8:30 AM Thread Starter
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Re: Bypassing 71 anti diesel & blocking relays

Thanks Art, will begin looking today. Your right about things coming loose (like the nut behind the wheel).
Have a good day,
tony
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