I've built a custom cooler with an A/C unit on it 2'x4'x7' cabinet w 2" rigid foam and lined with fiberglass RV siding (obtained for free from a local RV bulder, scrap pieces), most A/C units will easily maintain ales temps with no problem. I wanted to go colder at first I took the temp probe from in front of the cooling fins and moved it, took a Rancho controller for temp control, took a 7 watt night bulb hook to the temp controller and attached the temp probe from the A/C unit to the bulb by wrapping with foil which would cycle the A/C unit. Control at ale temp was easy, going colder was a little tougher, if large drop in temp was required the A/C unit would freeze up, but it was do able. I recently got a Coldbot from storeitcold.com I can now use the cabinet as cooler as well, this works so well I will be building a larger one for cold storage and serving draft beer from. My cabinet is in my detacted garage which in uninsulated during the recent high temps 105 outside, closed up garage 110 plus, with the coldbot, cabinet stayed within 1 degree of set temp.
Recently fermented three seperate 10 gallon batches of beer all at the same time during a recent heat wave, 3 15 gallon fermenters, each fermenter was wrapped with a heating blanket in case it got too cool and each with it own temp controller, each fermenter maintained it's set temp with a degree, once fermentation was completed cranked temp down to 40 degrees to cold crash before kegging the beers.
I've used refrigerators in the past which worked as well but running two refrigerators cost me more to run than the cabinet with the A/C unit and the coldbot.