I have an ac in my garage, but I find it better for most jobs to use a high volume fan like a chicken house fan or whole house fan, etc... I set it near one door and let it blow back into the garage and force the inside air out. The moving air evaporates the sweat and cools the skin. It allows the doors to be open.
Now if I'm going to be sedentary, like soldering or working on the bench and don't need the doors opened often, I use the ac.
For people down south that's probably a very reasonable response. Around here I only get 5-6 months of above freezing temps. Spring and fall, historically, can be pretty chilly. I keep the doors open as much as I can, but I also have to manage my heat.
I keep 90 gallons of water as a thermal mass, and rely on a lot of metal in the shop to hold heat as far into the winter as it can. prematurely cooling it seems counter productive.
In the winter, I keep it comfy with a 1500 watt electric heater, I can generally maintain +15C all winter long, for about 135 a month.. In the summer, I rely on air flow to keep in comfortable.
Edited by Chopperhed, June 26, 2015 - 10:32 PM.