A/C help on my 12v conversion

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silvercummins14

Georgia Diesel Mafia
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Jun 1, 2007
Messages
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I put a 12v in my 03 Dodge 3500, ive got everything working but the a/c. Im using the 12v A/C compressor and My 03 wiring harness. I cut the plug of my 12v wiring harness and put it on my 03 wiring harness where it would plug into my 12v a/c compressor. The a/c compressor will not come on unless you jump the relay which it will then come on but not cycle. I know there are some people who have done these conversions and got the a/c working. Open to any suggestions. Thanks
 
I don't know about the Dodge but the Ford's computer will not let the ac kick on unless there is a tach signal could that be the problem? I've seen guys jump it and just put a switch on the dash.
 
Are there any big differences in a older A/C compressor off a 12v compared to one of an 03 cr that would not make it work?
 
I'm just tossing this out there and may be completely wrong - I'd assume the newer AC unit would have different wiring or connection's (almost like a voltage regulator on the altenator) that would receive a signal from the computer to turn on and off/cycle whereas the 12 valve I once again would assume would not. Personally I'd use the newer AC Compressor if you are using the newer wiring harness and computer to run your engine/accessories. The 03+ Dodge trucks are much more computer controlled then the older ones (which you already know) and something as trivial as this could possibly be your problem.

Just tossing it out there.
 
I was planning on using the newer a/c compressor but it will not bolt up to a 12v block. So i put a 12v plug on my 03 wiring harness and ran the old compressor. Both plugs were two wires and actually the same color. For some reason the computer is not telling it to come on. may have to take it to a dealership and let them hook it up to there computer to try and figure it out.

I just figured there is someone that has already done this before. Maybe i wrong. lol
 
Maybe try connecting the old 03 AC Compressor back up to the harness (not installed on the engine, maybe just laid to the side) and see if you here the clutch click on and off while the button is pushed?
 
As stated the Ford stock ECM will have to see a tach signal to know the engine is running,I had to add electric pusher fans to cool at idle as the stock CR 05 fan would not engage.Good luck.
 
both the 12v and 03 have 2 wire ac coils, 1 positive. and 1 negative,and simple ohm test will determine which is which, if the 12 valve was a 94 and up then the compressors were basically the same, some clocked a little different, but will interchange. If you are having to jump across the relay or put power to the coil for it to engage, your problem is else where, low on freon, bad cycle switch etc......
 
I was going to suggest checking the system charge but Dan beat me to it. Also try jumping the pressure switch. If the alternator is charging and the tach works the PCM should be calling for it. May also be the Climate Controls in the dash.
 
Ok. I've got freon in the truck, but my computer is not reading any pressure. Put a new sensor in it and still no pressure reading. Any ideas?
 
I think your problem is that the 03 system is computer controlled and the cycling is controlled by the 03 engine computer which is gone. A 12 valve system uses a low pressure cycling switch whichs works only by the pressure in the system to turn the compressor on and off. You will need to incorporate a cycling switch used on a 94-97 12valve to make the compressor cycle.
 
On mine the pressure switches went to the computer and the the computer controled the the relay. SO I took the computer out of the system. I used the the pressure switches to control the relay. The computer sends a ground signal to the relay and the presure switches use a positive signal to the computer. So now the wire goes from the pressure to the relay coil and the other side of the relay coil is grounded.
 
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