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Discussion Starter · #1 ·
Guys,

I'm replacing the wiring in the engine compartment of my 70 GTO during a rebuild and I have a question. This is a factory AC car but the AC was totally rebuilt several years ago and although most of the wiring is still factory, several of the connector harnesses were replaced, probably with whatever the guy in the AC shop who did the work had lying around. Since that rebuild the AC has worked fine. With the engine out now I've decided to replace all the engine compartment harnesses including the AC stuff. My question is, the current wiring for the system is different from the factory set up. In all the manuals and wiring diagrams I have there are no factory wires to the POA valve that I can see, but my current system, that again worked fine, has been re-wired to have a wire go from the compressor to the in-board terminal on the POA valve and another wire from another connector, the purple wire with white stripe (not the factory color I'm sure) in the "T" connector seen in the pic to the outboard terminal of the POA valve. I have attached several pics to clarify. How can I rectify this? I suppose I could splice in new wires into the harness to the terminals where they originated from in the current set up, but then they would still have wires in the system that apparently are not in my current set up providing power to god knows where. Any assistance with this is appreciated.

MIke

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Old(s) Fart
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Well, the first thing is that your shop converted the A/C to a clutch cycling system, as evidenced by the aftermarket POA eliminator tube in the first photo. That means that the factory harness won't exactly match up with your current system. Also be aware that the massive A6 compressor was never designed to be used in a stop/start CCOT system, despite the fact that GM did exactly that in the late 1970s. Compressor life suffered as a result.

 

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1949 Ford Coupe RESURRECTION
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Joe is correct. The "new" wires appear to be a simple interruption of the compressor clutch wire, with the electrical device being a pressure switch to cycle the compressor. If you are going with a modern compressor, it should work fine just by cleaning up the ugly job that someone else did.

Here is a good write up of how it works:
 

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Discussion Starter · #4 ·
Joe is correct. The "new" wires appear to be a simple interruption of the compressor clutch wire, with the electrical device being a pressure switch to cycle the compressor. If you are going with a modern compressor, it should work fine just by cleaning up the ugly job that someone else did.

Here is a good write up of how it works:
Thanks guys. Would it be hard to convert it to a factory set up so I can use the factory harness? What would that entail? Would it just mean replacing the poa valve with a factory one?
 

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Old(s) Fart
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Thanks guys. Would it be hard to convert it to a factory set up so I can use the factory harness? What would that entail? Would it just mean replacing the poa valve with a factory one?
You can reinstall the factory parts, but the POA valve needs to be recalibrated for R134 if that's what you're using.
 

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Discussion Starter · #6 ·
No I'm using R12. I still have a bunch of cans lying around and never converted the system. OK so if I just replace the POA valve with a factory piece I can use the factory harness?
 

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Old(s) Fart
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No I'm using R12. I still have a bunch of cans lying around and never converted the system. OK so if I just replace the POA valve with a factory piece I can use the factory harness?
Yes. I assume the car still has an A6 compressor?
 

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Discussion Starter · #8 ·
Yes I believe it is. I attached a pic. The other thing is that I have dual electric fans that were wired into the compressor switch (as well as a thermostat) to turn them on when I put the AC on. I guess I can just splice into the same compressor wire the AC shop had re-routed to the POA valve, right?


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Old(s) Fart
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Yes, that's an A6. The compressor clutch just gets a 12V signal to engage. You can tap into that to operate a relay to turn the fans on.
 

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Discussion Starter · #10 ·
Yeah that's how I had it before. I'm thinking now of keeping the newer POA valve and just getting the two wires from the new harness. The car get's driven very little so I'm not terribly concerned about compressor lifespan. My question is, the AC shop had the wires running to other places than the factory harness does. Do I cut the wire outright in the new replacement factory harness and tape over the unused end or should I access the wires I need in the new harness for the POA valve with T-splices?
 

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Discussion Starter · #11 ·
Never mind. I get it now. The only thing the AC shop did was the re-routed the compressor power wire to run through the POA valve. If I cut the compressor wire at the engine wall in the new harness I can neatly incorporate a new wire into the replacement harness and run it to the POA valve, as well as run a return wire to the other end of compressor wire so that I can still connect to the compressor with the OEM style compressor plug. I'm guessing that the AC shop I took the car to did it this way because the OEM POA valve is probably pricey and harder to find than the newer one.

This is the easy part. The hard part will be getting the rest of the system up and running. Both here and the forum that 49 Ford posted earlier will undoubtedly be valuable in navigating the flushing, vacuuming, and charging of the system. Thanks for the help.

MIke
 
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