The coil on my inside unit is freezing up and I am trying to find the fix. So far what I have came up with is, I am either low on freon, dirty coil, freon leak, or thermostat on inside unit(but unlikely). I had a friend that does HVAC on the side come buy and check my freon and it was at 20psi so he filled it to 65psi, but didn't test it for leaks. It seemed to take care of the problem for a few hours but then it went down again. I thought my coil was clean but after inspecting it better the under side of it looks gummed up with black gunk between the coils. I have tried to spray some houshold cleaners in it to atleast break it up some with little success. The fins look good(not bent). I am going to get some real coil cleaner and was curious what is good to use? Also, what does it take to remove the coil and clean it? If I unhook it will freon blow out everywhere(providing that it hasn't leaked out)or is there some kind of valve that keeps the freon in(I'm sure it is unlikely)?

Also, I don't have the proper guages so if I was to use a tire guage and test the pressure on the freon will I get some kind of idea how much is there? I don't need an accurate reading. I am mainly trying to see if the freon that was put in leaked out. Thanks, Chad