No Idle Change with A/C On

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bohica2xo
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Re: No Idle Change with A/C On

Postby bohica2xo » Thu May 31, 2018 9:48 am

The PCM is definitely not commanding a compressor start.

If you look at the relay circuit you posted in the other thread, you will see that the clutch relay coil is always hot with the key on. The PCM grounds the coil to activate it. They low side switch things because N channel parts are cheaper & easier to deal with. That started with EFI injector drivers, and has spread as the computer takes over other functions.

Don't worry about testing for the PCM signal at the relay.

You appear to have enough refrigerant to see a compressor start. A low system will show acceptable static pressures, but begin short cycling immediately. Some PCM's will lock out the compressor with too much short cycling.

You say that the refrigerant pressure transducer readings are not in range - that is a problem. How far off is the output voltage? That alone would cause a lockout.

Evap sensors usually hang in there. 2 wire NTC's are tough as hell. usually a failure is a broken wire.

The sunlight sensor is a low order input - the system works in the dark anyway. That sensor allows the PCM to guess at heat load, and let the compressor run to different parameters.

The first thing I would look carefully at is the out of range transducer. If it is beyond the +/- 2.5% and LOWER than expected pressure - swap it out.

Finally, the code reset. This may sound pedestrian, but try disconnecting the battery & going to lunch. I don't know what the korean devils may have done with the PCM but that works on some american stuff.
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lothian
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Re: No Idle Change with A/C On

Postby lothian » Thu May 31, 2018 10:09 am

I'll recheck the transducer at first opportunity. I'm uncertain of my initial check anyway.

If this sensor (and the others) test OK, I'll intuitively suspect the climate control console before the PCM. It'll suck if that thing is flaky.

As for the "code reset"...
I should have listed doing that among the cursory check-off items in my earlier post. I've had the positive terminal off its post a few times for this and other (lengthy) repairs.
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bohica2xo
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Re: No Idle Change with A/C On

Postby bohica2xo » Thu May 31, 2018 5:14 pm

Back probe the sensor circuit with it connected in the car. With the engine running check the 5.0 volt reference voltage to the ground terminal. If you get 5v then both the reference voltage & the ground are good.

Then check the output voltage to the ground wire. I glanced at the FSM formula, and it looks like there is a conversion error someplace. Most any sensor like that should be around 1.0v at the lower end of it's range. The automotive environment is not friendly to 200mv signals.

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