TXV vs. Fixed Orifice (Piston)
A fixed orifice is a drilled hole: right at exactly one set of conditions, an approximation everywhere else. A TXV adjusts refrigerant flow continuously to hold superheat where it belongs.
In a stable climate the difference is modest. In mountain swing seasons — 40° mornings, 80° afternoons — the TXV's ability to protect the compressor from floodback and keep the coil fed pays for itself in equipment life and steady capacity.
Charging differs: piston systems charge to superheat, TXV systems to subcooling. Knowing which you're standing in front of is the difference between charging a system and wrecking one.
Most modern matched systems ship TXV, so the question mostly arises on older equipment and coil swaps — where upgrading the metering device during a coil change is cheap insurance.
Whichever way the job decides, it's on the shelf in Asheville with same-day pickup.