Neither of my 1106C compressors will run. no motor hum. It's like I have no elec. power to the units.?

it's as though I have no elec. power to the unit's. Probably something simple but my user's manual is not very clear and the diagrams aren't very usefull. I'm thinking the problem may be an issue with the regulator knob. There are probably less then 2 hrs on either unit. I bought them in 2007 and gave one to my son.....