Gas and Oil Home Heating Furnaces - Outside AC unit won't turn on

My furnace turns on with the thermostat, but the outside unit won't even make a noise. I have tried the circuit breaker on the inside, and the cuttoff on the outside. What might be the problem?

If you are sure that the outside unit is getting power, then listen for the contactor to close when the indoor unit comes on. (make take two people). This is a relay that is controlled from the thermostat to provide AC to the compressor and fan motors. If you hear nothing, check the small wires running to the unit to make sure that they aren't cut or chewed on (weedwacker or dogs chewing on it). If they are in good shape, you may have a bad thermostat, or contactor.

Also some thermostats have a built in delay for the compressor, in otherwords, it won't allow the condenser unit to come on if it has not been off for at least 5 minutes or so. This is to protect the compressor motor. So you might have to wait for that delay to clear to listen for the contactor closing if you miss it the 1st time. You can check for the control voltage for the contactor coming from the thermostat, but you can be exposed to high voltage components in doing so. If you aren't familiar with this stuff, I would not recomend going near it.