Corny kegs, and actually all metal kegs, are single wall construction. Where are you measuring the temp of the beer? If the kegorator has a tower for the taps, then chances are the beer is getting warmed up significantly as it goes up the tower. If there's no fan blowing cooled air up into the tower, or some other way to get the cooling up there, then you need to address that. Trying to reduce the temperature inside the kegorator will freeze the beer lines on you. It will also, probably, freeze the kegs if you go below 32F inside.