Checking refrigerant charge by superheat is typically done on systems using __________.___

Checking refrigerant charge by superheat is a method primarily used in systems with fixed orifice metering devices. With fixed orifices, the refrigerant flow is constant and does not adjust based on the load. This allows for an accurate measurement of superheat, as it indicates how much heat has been added to the refrigerant as it leaves the evaporator.

Superheat is the difference between the saturation temperature of the refrigerant and its actual temperature at a certain point in the system, typically measured at the compressor inlet. In systems with fixed orifice devices, technicians can easily monitor superheat to determine whether the refrigerant charge is correct, as these systems rely on a consistent refrigerant flow that does not adjust dynamically.

In contrast, expansion valves, capillary tubes, and thermostatic expansion valves introduce complexities such as variable flow rates and dynamic adjustments that can complicate superheat readings and their correlation to refrigerant charge, making them less reliable for this particular method of charge verification.