It sounds like you're trying to beat the heat in your garage! Have you considered a mini-split air conditioning unit? They're a bit pricier than a window unit, but they offer a more permanent solution and don't require any venting.
Hot 2 Cold Air Conditioning might be able to help you out with that. It's great that you have a thermometer to track the temperature, as that will help you determine the right size unit you need. Good air conditioning is key to the well-being of anyone in the house. Good luck with your project! And I hope you manage to finish it well.