Hi! I am a young homeowner (about 2 years now) and when my wife and I were getting the general inspection it was noted that our AC used R-22 refrigerant and might need to be replaced if it started leaking. After hearing how much it would cost to replace a system (and having some ideas of my own for improving IAQ) I have started down the road of getting prepared for a DIY replacement should that happen in the near future. From reading a few posts it sounds like getting the universal EPA 608 is a good first step. Are there any recommendations for online training courses that teach the material well? A quick search showed SkillCat but I am curious if anyone had any preferences.