Since '99. Certified in A/C class 1, 2 & 3. Work on rail cars, multi unit, multi ton, multi zone cars. Certified on 7 different rail cars spanning from the overhauled retro fitted steam & desil cars to the latest cars from American manufacturers.
The masters released digital self controlled thermostat to mechanical click one and offs.
Certified for bridges, tunnels, and huge buildings like the Empire State Building down to in window house units.
The first thing to understand is what a BTU unit is and how much it can cool. I'm not going this get into a lesson here. Please just take my word for it. Or loose money on it.
Best bet, hands down, is that cooling T shirt I mentioned earlier. The T shirt has tubes sewed into it that travels all over, front and back, neck collar to the bottom. Cool water circulates through the tubes. The reservoir can be ice chilled. The set up has a bucket (for lack of better adjectives) the head odd thenice and water. A small pump circulates the water around your body core. Once your core gets cool, it will act like the refrigerator for the rest of your body.
Basic thermodynamics and human physiology.
It isn't A/C but it is an effective way to stay cool.