Bought new 7 gallon 1HP horizontal craftsman compressor. Used first day worked great . Second day plug it up hit on switch and all it does is click when you cut it on and make a humming sound

SOURCE: Sears Craftsman 3-Gallon, 1.5 HP Air Compressor Hums

YES IT MAY BE THE CAPACITOR . IT COULD ALSO BE THE WIREING IN THE MTR, THE PUNP ITSELF.

SOURCE: Craftsman 25 gallon compressor wont cut off

The pressure switch has snap action contacts that are opened by a diaphragm pushing against a spring mechanism. Unplug the compressor and remove the cover to the switch and look for the contacts. Make sure that they are not welded together from use. Move the on/off lever to see if they open and close. You may have welded contacts or broken mechanism within switch. A factory replacement is expensive, however if you are a tinker-er you can use a lower price generic pressure switch available on ebay. Switches are sold by pressure range, you need a 120#. Fittings may need tweaking. Enjoy

SOURCE: air compressor not working

If your motor is running and not the pump, the malfunction is either in the pump or the coupling between the motor and the pump.

Some of these compressors are manufactured so cheap now that there can be just a set screw that is loose and the motor shaft is spinning free inside of the crankshaft.

If you drain the oil out of the pump and take off the pump crankcase cover, you should be able to see the problem.

SOURCE: Air compressor won't go over 40 psi?

my ace air compressor which is 26 gallon 5 hp will not get over 60psi what is wrong with it please?

SOURCE: I have a Craftsman 3 gallon 1HP air compressor

Sounds like the compressor has failed -- probably the valve -- tear down and rebuild is probably the solution, or replace compressor, or just buy another unit. My nature would be to tear it down and see what's going on.