learning sealed systems has rewards beyond domestic refrigerators.
Although understanding sealed systems will help in diagnosing of domestic appliances.
But a good understanding will help in diagnosing Hvac systems , walk in coolers, ice machines, and even automotive.
!!!!! DO NOT!!!! enter in all at once. Get some tools and buy some refrigerators on the side and fix them and sell them. Kind of a pay for your play time. Slowly learn the brazing techniques (in tight areas) , how to protect surround wiring and plastic components, and the ever critical Super-heat and sub-cool. Learn this stuff to help in diagnosis, even on domestic units. Sealed System can be profitable if you are thorough about ruling out leaks and if you have a good understanding on how they work.
After about 3-5 years you can work into a place where you can do hotel ice machines, florist coolers, soda machines, it just can really open up more oppurtunities.