I have gone through that exact thing. Few years ago it hit like 102 and we had to unload a trailer. Work outside for 2 minutes sit in AC for 20.went back in the AC, cooled off welded that piece, then back inside.
Afterwards I talked to a friend of mine that works out in it all the time.
He said you really need to be out in it all day and every time you step into AC it is a huge set back in your body's adjustment process.
Even though I am now old, he was right. If I start my day at a decent time and stay outside I can work all day and ignore the temps, but just sitting down in the AC for lunch is enough to **** my entire day.
The only thing that stops me now is trying to keep sweat out of my eyes. Dang seems impossible some days.