the txv valve is a metering device which either increases the flow of refrigerant to the "a" coil or decreases it. by doing this it keeps the a coil from freezing up. so if you compare this to a garden hose, more water flows without a nozzle, but sprays with more force with a nozzle. this may work for you, i'm not sure. my 3-1/2 ton unit has 3/4" copper, so you may be good to go.
good luck, dan