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Q: ac will not come on, clutch will engage

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last trip out ac was working perfect until I shut it off for a minute. When I turned it back on-nothing. When I stopped to look it over I saw the fan was locked up. So I replaced the fans as a unit, but the ac will still not come. I switched the relay with the wiper relay, still nothing, checked for blown fuses, found none.Then on line a read that it might be the transducer. That when it goes bad the clutch will not engage. I can buy one of those cheaper on line than at any shop. I also tried resetting the system by disconnecting the battery, but again-nothing. Any ideas ?

My car has 175000 miles.
My car has an automatic transmission.

The powertrain control module (PCM) receives input from sensors to determine compressor control. The first thing you want to do is make sure power is getting to the compressor. You can do this using a test light or digital multimeter. If there is no power getting to the clutch, suspect a faulty relay, A/C pressure switch (transducer), wiring, low system pressure (insufficient refrigerant charge), or a blown fuse. The PCM could also be to blame since it directly controls the compressor clutch relay, but its not likely. You can also check the ground side of the compressor circuit using a test light or multimeter.

If the compressor has both power and ground but it does not engage, the clutch, coil, or compressor have failed. Try turning the compressor clutch by hand - if it turns, the compressor is not seized and either the clutch or coil are to blame. Trouble shooting an A/C system can be difficult, so I suggest you give the professionals at YourMechanic a call.

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