[Bob Cook]

Ron

Clutch is normally de-energized. You can take a couple of cables and apply voltage directly to solenoid (12v not 24volts) and you should hear it energize. (disconnect the harness plug on the aircraft at the compressor solenoid.

You can take an ohm meter and see there is current in one direction and not the other. if there is a short in the diode you will get a very low resistance in either direction (reversing probes).

You need to find out it the diode is on the compressor or in the harness at the compressor. It is used to cut the reverse EMF (energy) which destroys the switch as the coil is an inductive load.

You can measure the resistance on the one in your car and it should be the same as the one in the aircraft. Should be just a few ohms.

The schematic is really simple. The voltage (24v) is fed to the switch in the overhead and then goes to the thermostat switch then to the solenoid (also thru a low pressure cut out switch which is normally closed when system is pressurized). It is that simple.

It is rarely the coil in the solenoid would short. more likely the solenoid or the wire is chaffed and is shorting to ground somewhere between the thermosat switch and the solenoid.

Remember to do the test with the thermostat off and see if it blows the breaker when the thermostat is moved towards cool (should hear the switch click when it is moved and is calling for cooling).

hope this helps.

Bob