I once had this problem with my 2000 Nissan Altima. It wouldn't turn on and I went to a bunch of mechanics and they said they couldn't find anything. All I had to do was replace a little part in my evaporator coil called the "TCA" or Thermal Control Amplifier. See if you can get one. It tells the compressor to turn on and off. I'm unsure your car will have one but I hope his helps!
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