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AC wiring

 
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Sat Sep 20, 2014 11:15 am    Post subject: AC wiring Reply with quote

4th gen compressor in a 3rd gen car. Anybody know how to set this up without a PCM? The only wires I am starting with is what comes out of the firewall from the HVAC head unit.
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aaron_sK
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Joined: 23 Jan 2006
Posts: 8834
Location: Back in beautiful Tacompton

1987 Chevrolet Camaro IROC-Z

PostPosted: Sun Sep 21, 2014 3:08 pm    Post subject: Reply with quote

The 4th-gen compressor itself is just as dumb of an animal as the thirdgen unit.

Usually wiring a compressor is the least of your worries in an A/C retrofit. What are you doing for the rest of the system?
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QwkTrip
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Joined: 17 Feb 2004
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Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Sun Sep 21, 2014 3:17 pm    Post subject: Reply with quote

Everything else is thirdgen. I may have inadvertently eliminated something so I need to know the general strategy how it works.

I get the idea I use the AC request from head unit to run field coil on hi and low pressure switches, and the contacts for those switches enable the AC compressor. That way if either of those pressure switches open then the compressor clutch opens.

Is it really as simple as that?
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aaron_sK
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Joined: 23 Jan 2006
Posts: 8834
Location: Back in beautiful Tacompton

1987 Chevrolet Camaro IROC-Z

PostPosted: Sun Sep 21, 2014 3:57 pm    Post subject: Reply with quote

QwkTrip wrote:
Is it really as simple as that?


Pretty much. There is a diode on the compressor feed, and a trigger wire to the ECM which IIRC is just there to trigger the fan and idle kicker.
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chevymad
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Joined: 11 Jan 2004
Posts: 5472


1987 Pontiac Formula

PostPosted: Sun Sep 21, 2014 5:12 pm    Post subject: Reply with quote

Is the high pressure switch normally open or closed on these? I've seen them daisy'd with the low or with the clutch ground run through it.
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Sun Sep 21, 2014 10:19 pm    Post subject: Reply with quote

I wonder if the flyback diode is integral to the 4th gen compressor?

Where was the diode located in the original 3rd gen harness? I might be able to find my old one but could use some hints. Guessing it is wired right in the back of the original plug to AC compressor?
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aaron_sK
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Joined: 23 Jan 2006
Posts: 8834
Location: Back in beautiful Tacompton

1987 Chevrolet Camaro IROC-Z

PostPosted: Mon Sep 22, 2014 6:41 am    Post subject: Reply with quote

Yes, the the thirdgen diode is attached across the leads of the connector. The fourthgen diode is inline but very close to the connector IIRC.
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Mon Sep 22, 2014 6:36 pm    Post subject: Reply with quote

I found the 4th gen flyback diode. It is inside the body of the connector. I can't see it but the terminals test out with a multimeter.
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