I hear ya. My enlargers and Jobo equipment are currently in my un-air conditioned garage. I have been using it this way for quite some time. My main purpose in wanting to build a darkroom within the garage is to be able to have A/C. The winter time is bearable, but even after the sun goes down in the summer, the garage/darkroom feels like a sauna all night long.
Though I spoke to a friend at work yesterday who informed me that his friend bought one of those roll around portable A/C units that he claims does a good job at cooling the entire garage down.... Hard to believe but interesting! That could fix the heat problem, but dust control and having to open the big garage door every time I want to wash a batch of prints would still need to be addressed. And then there is the fact that I now have a big revolving door standing in the middle of my garage... I had better build that darkroom!