First off this is a sears unit digital thermostat, 5 ton unit I think. Turn a/c on it hums but no fan comes on. The relay kicks on but after that I am lost.

Possible bad capicitor

Look at it see if the top is buldged up,should be flat not poped up

Nothing burnt or out of round or anything

You may not have high voltage to the unit, did you check breakers?
Do you have a multimeter? The contactor may be what you hear humming