A/C clutch not turning on

  • 3.4L
  • V6
  • 2WD
  • 190,000 MILES
I’ve vacuumed down the system to -30 for 1 hour. Let the system set for 30 minutes to insure no leaks. Replaced Freon and PAG-46 oil to spec.
Pressures are ~73 L and ~73 H without compressor running.
Pressures are ~30 L and ~225 H with compressor running.
The only way to get the compressor to come on is by disconnecting the A/C pressure switch and then plugging it back in. I’ve replaced this switch thinking it was faulty, but have the same issue with the new switch as well.
Could it be a faulty computer?
Any help would be appreciated, thank you in advance!
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have the same problem?
Saturday, August 7th, 2021 AT 10:25 AM

1 Reply

Clearly the pressures are perfect so good job with that. See the chart below for pressures based on ambient temp for future reference if you need them.

However, based on the fact that the compressor will only come on when you unplug the pressure sensor just means we have a control issue. Basically when the sensor goes open the ECM defaults the compressor on and then will cycle it. This is just so that the compressor will dehumidify the air so that the windows don't fog up.

What we need to do is check the voltage at the sensor on each of the 3 wires.

You will have a 5 volt reference wire. This will normally be about 4.5 volts. Then the Low reference wire is basically the ground and will be around .5 volts or the different from 5 volts and the 5 volt reference wire.

Then the signal wire is going to vary based on the pressure in the system. This is how the ECM knows what the pressure is and when it is not to high or low, then the ECM grounds the relay to turn the compressor on.

So let's start with checking the voltage on each and go from there.


The wiring diagram is below as well. Just use a paper clip or something small that can back probe the connector. Please let us know what this is or what questions you have and we can go from there.

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Sunday, August 8th, 2021 AT 4:21 PM

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