I don't know if the EPA test has changed in the decade since I took it, but it was very easy for me to get the cert needed to buy refrigerants myself. I found an A/C supply store that administered the tests, found a study guide on the internet, ready the study guide in half an hour, took the test. Now apparently you can do the test online whereas I had to go to the store.
At the end of the day the problem was the evaporator blower motor. It was insidious because it certainly worked and moved air around, but it was something like a 3 speed motor and the 2nd speed was failing and not moving enough air around, hence the icing and not producing enough air, something like that.