Techs? Possible link between A/C and ignition coils??

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Timmah

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I had a P0351 code last week and the AC stopped working on the same short trip.

P0351 is something wrong with the ignition on cyl #1, tested power and coil, the coil had continuity no resistance.

But

When I replaced the coil (I did nothing else at all) the AC started to work again

Is this a coincidence? or does the computer do this to limit load on the engine?
 
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The coil wire is probably grounding out on the metal a/c line. My #4 coil wire was rubbing on the a/c line near the firewall and was grounding intermittently for over a year before I figured it out. Put a piece of corrugated wire loom over the wire after I fixed it.
 
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Cylinder #1 on the 5.4L is on the Right Bank (passengers side). The AC system components are situated across the passengers fender inner liner. If I remember correctly the pressure sensor switch for the high side AC line is located, in that general area. You probably moved the connection around on that switch, while installing the coil, causing it to make contact and allowing
the AC to function.

The other thing you might consider (and I don't have the harness diagram in front of me) is the fact that the AC pressure sensors share ground with the coil system. If that's true, then you might have a problem relative to that ground. I would suggest looking at that circuit in your wiring diagram and tracing/testing it on the vehicle.

The computer does unload both the AC compressor (and in some cases the PS pump) during idle, when it reads (X) load on the system. That normally occurs when its raining outside and you have all many electrical devices in operation at one time (lights, wiper, radio, defroster etc.). The purpose is to raise the alternator output by eliminating large power consumers in the system.
However this change is temporary and the AC compressor will restart the moment you start moving again.

The final thing to consider is did you remove the battery cable when changing the coil. Removing your battery cable will cause the system to reset "Learn Mode" in most cases.
 
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