Originally Posted by SonicVQ

I'm glad you didn't try to jump any wires... It isn't a switch, but a pressure sensor.

I suspect your A/C refrigerant is low and the ECU isn't turning on the A/C clutch to prevent damage. If the pressure sensor detects less than 17 psi or more than 452 psi, the ECU will not turn on the compressor.

If your scan tool has advanced diagnostics, it can show you the voltage, or use a meter to check. It should be between 1-4 volts.

The center wire is the 5 volt sensor output. The outside wires are ground and 5 volts. Use a meter to determine the polarity and check the voltage between the sensor ground and the centre wire.