A technician checks the charge on an R-22 system that uses a fixed orifice (piston) metering device. Which measurement is the primary method to verify the charge?

Explanation

On a fixed-orifice system, superheat is the primary way to check the charge; the technician compares measured superheat to a target from the manufacturer's chart. Subcooling is the preferred method on TXV systems, not fixed-orifice systems. Superheat is the difference between the actual suction temperature and the saturation temperature at the suction pressure.