Air con (by 2 users)

Could be the thermostat or the low voltage line to the outside. Usually a dog chews through it or the weedeater hits it and breaks connection. Turn on cool, go outside and see if it gets 24 volts to the two wires going to contactor (have to take off cover to get to it) DO NOT TOUCH THE CONTACTOR IT HAS 240 V AT ALL TIMES, unless disconnect is thrown, so turn it off. If you aren't getting anything, then it's either the low voltage wire broken somewhere or the thermostat malfunctioning. Make sure you turn off the inside unit before messing with thermostat or you will pop the transformer. If it pulls the contactor in, and you still aren't getting anything, then check for voltage on the load side of contactor (opposite from the inlet or lead side). If you are and you hear a hum from the compressor and the condensing fan motor is running, then it's your compressor. You'll have to remove the top cover to do the next step. Check to see if it when to ground by using a meter set on resistance and with the connector to the compressor removed, put one lead on one of the copper pipes going up to it and touch the other lead against any or all of the pinouts on the compressor. If you get a reading, it went to ground and you will need a new compressor or whole new condensing unit, depending on the age of the one you have now.