I'm an environmental chamber technician. I fix and test the equipment that does all of the temperature and humidity testing for most electronics from consumer grade stuff to stuff that is literally going into space. Basically an environmental chamber is just a programable box that is refrigerated and/or heated that you put stuff into to see how it performs at different temperatures. The ones I work on also often have programable humidity levels for testing equipment under basically any normal atmospheric conditions. The ones I work with are anywhere between the size of a household microwave and slightly larger than Volkswagen Beetle. The ones that don't use liquid nitrogen can manage temperatures anywhere between 200C and -75C. The liquid nitrogen ones can of course manage temps as low as liquid nitrogen gets.

As far as education and certifications go, there isn't much. In the US you do need an EPA 608 certification to work with refrigerants but that only cost like $100 (my employer covered it) and it's a lifetime certification. Everything else was just on the job training. I just got mentored by some coworkers, did some independant study, and practiced. The biggest thing is just haveing a technical mindset. Troubleshooting is troubleshooting so basically if you're someone who can usually figure out how to fix things on their own then odds are you could do my job with minimal refrigeration training.

As far as getting into the same niche today, I definitely would if I could find the job (it's not all that common). I love working with refrigeration and troubleshooting these machines scratches tha puzzle solving itch in my brain. It's fun to see the unique options that certain customers get like water cooled systems or liquid nitrogen boost units. Also seeing as how these machines need to be benchmarked at a known ambient temp, it is one the very few refrigeration related jobs that you get to do from a strictly climate controlled building. It is always exactly 23C in my work area because that's exactly what our testing spec calls for. To top it all off the pay isn't bad. I could be making a bit more in normal HVAC but not much more and, unlike HVAC, my equipment comes to me in my climate controlled shop. I don't have to climb up on a roof when it's 40C outside to fix someone's AC.