HVAC-R tech is a welder, plumber, electrician, and troubleshooter all wrapped up in one individual....LOL
The sciences involved with all of the different gasses, heat exchanging due to gasses changing states under pressure or in a vacuum and all sorts of neat stuff to challenge your mind.....
The one classroom experiment that we did that sticks out in my mind was drawing out all of the atmosphere out and watching water freeze and boil in the same beaker.....
We sealed the rim of a glass bowl down to a pane of glass with putty...inside we had the beaker of water sitting on the glass pane with a thermometer in the water to measure the temp of the water. The bowl had a hole in the bottom(now top) where we inserted a hose(also sealed with putty) and then pulled a vacuum with a vac pump.....when we got it down to 27-28" of hg the water started boiling and freezing at the same time even though the temperature of the water remained a constant 70 something degrees F. Weird seeing it ice over while boiling, it would boil so hard that it would break the ice and start all over again....