I can see from your replys you know what your doing and are experienced. I did hating and cooling work back till 83. I am now trying to get back into the trade and enroled in a adult ed. School. I have to say it was a waste of $5000.00. All I really got out of it was an EPA certificate. Controls (elect) are no problem, its this new super heat etc which we never used back then Basically a more precise charging method to me. My question. In my own home I'm getting ready to install a new a/c unit. It's a 3 ton, but I needed a 2-1/2 ton. I plan on changing the compressor to a 2-1/2 ton, figuring that's actually what seer is, a larger coil. I also want to install a heat exchanger, change the piston type orfice to a TXV, and install a receiver. The receiver only because it will help not being so precise in my charge. What do you think? I'd appreciate any input.