I have a 5hp 26gal campbells it hums when u turn it on it will either trip the 20 amp breaker or it wil start up most of the time it trips.is it that the breaker is too small or something else.please help.

Could be a couple of things, first, a cord, It might be a 20 amp breaker but if it goes through a cord, it loses amperage and will not start. It needs about 16 amps to start and then about 13 to run. Will it start by being plugged into the wall? Second, let the air out and see if it will go, too much back pressure, not enough power. third, make sure it is warm, We used to heat a bathroom on the job just for the compressors in the winter, of course we all went in there to at break time, only warm spot in the house. And last, If the capacitor is bad, it will lose it's power, but I would check the rest first. Hope this helps.