Keep your options open.
Warm and cool are relative terms that will change based on the activities you are doing. If it's inside the vehicle you'll be fine regardless of the conditions. Simply close the doors and it will heat right up.
Remember to keep it ventilated. Don't succumb to the temptation to seal the garage. You want to keep that air flowing and have the ability to rapidly turn over the entire air volume with minimal restriction.
This is where having a variety of lab coats can greatly help. They come in different levels of breathability and thickness. Maybe this goes without saying, but the first 20 minutes or so of working in the garage will be defined by your core temperature. Once that swings one way or the other you'll start to feel unomfortable. Keep that core temperature where you want and the rest of the paths get easier.
Modify the garage temperature
Drill a hole in the wall and use a combined portable ac/head unit. These will drop or raise the temperature noticeably on most days. On very hot and humid summer days, it will take about 6 hours and then the apparent temperature will drop 5-6 degrees in the garage. If you open the doors you'll have to start all over.
The biggest challenge here is installation. Find about a 4ft high area to penetrate the wall for the vent. Put a screened dryer vent on the outside. Mount the AC unit itself higher up - the author has it in the back of the garage, and so has it on top of a mini-fridge. This is key as these will put out about a glass of water every 30 mins when operating in the summer. You need to fit a drain system to the plug on the AC unit. You can simply gravity feed it right out the door of the garage and stuff the tube through the side. Alternatively you can drain into a bucket and empty it occaionsionally. Don't open the main doors though, as all that cold air will leave. The convenient solution for the author was to add a T-fitting to an exposed auxillary house AC drain line and drain directly outside.
Make sure you invest in a variety of ducts of various lengths and some gorilla tape. These will allow you to make improvised and semi-permanent seals, as well as direct the air where you want it.
Modify your body temperature.
The simplest thing you can do to warm up or cool down is lay down on the concrete slab. It has a relatively stable temperature of 55-60 degrees year round and has excellent thermal conductivity. Get as much of your body in contact with the concrete as possible and you'll find yourself staying cool even when the air temperature is above 80.
Get fans, lots of portable fans, that helps. Get high powered nearly silent fans that are positioned over your most common workplace, that will cool you down fast. Make sure your portable AC unit is on wheels, or add custom ductwork. Blowing the cold air directly over your body is a huge help and if you're working inside the vehicle.
Ever tried an ice-vest? They add a few minutes to the core temperature warm up delay. They are impractical, but if you have and extra 2 hours every time it it needs to refreeze and want to work for about 40 mins before your core temperature warms up, it does work. Same with a simple ice-cap. Put a cold pack in it instead of the recommended ice cubes as the ice will leak over you and shift around as you move your head. The ice does have better thermal conductivity than the cold pack, but it's generally moving so much it's not worth it. If you're serious, you can invest in the same system race car drivers and medical professionals use: a Cool Suit. It would be great if there was a cost effective system here that actually worked. Alas, the best you can hope for is about 20 minutes of comfort and then be having so much fun you distract yourself from the discomfort later.
The biggest hassle with over-heating is probably the moisture on the work surfaces. When you are dripping in sweat it can be very difficult to hold anything. This is where the lab coats come in again. Have a full-covering lab coat gives you something to wipe your hands on quickly, and only adds minor discomfort from overheating.
- Winter lab coat Bulwark Fire Resistant Shop Coat
- Summer lab coat Lighter ESD Lab Coat
- All other times ESD Lab Coat