When A/C comes on the evaporator blower comes on but neither the compressor or fan outside start. Got 120 at each leg on line side of contactor. Every 20 seconds or so the contactor buzzes for several seconds then stops (trying to start compressor, I guess) and is humming continuously. Figure it has to be contactor or dual capacitor. Any way to know for sure? Capacitor looks normal, no bulges or splits. Thanks in advance for your thoughts on this.

denman

Did you check breaker in breaker box,, sounds like you have low voltage (24volts) coming from furnace but maybe no high voltage (230V),, just a thought

Didn't bother checking at panel as I had 240 at the cut off switch next to outside unit, I have 120 volts on each leg of the contactor inside the unit.

OK,, didn`t see that(probably there) in the first note,sorry, so now is the contactor engaged by low voltage? If so do you have the same high voltage coming out the other end, 120 volts at each leg?, if you do you could still have a bad capicitor, they don`t always show up bad just in looking,, you might remove and take it somewhere to have it tested,

Wrproop,thanks for the responses.
I do have 120 one both load legs. I'm going to take capacitor to get tested. Thanks again