Just want to let people here know that if you have an older system without a TXV you should seriously consider retrofitting. I am surprised that anyone would not see this to be true. I formerly had a fixed orifice metering the refrigerant and the system suffered miserably. I posted videos (look my name up and prior posts) and never did I hear that the TXV would help. I was trying to convince some here after researching endlessy that the information seemed to be pointing to a TXV. After installing one the frosting up of the suction line ceased and the compressor hums. No more temperature drops. I had 100 degree output on a 30 degree morning! So let me be the one to tell you, go TXV!
Here is a link to show you what I mean, goes for Heat Pumps as well. Don't over think it, you will not regret installing one.