A superheat check measures the temperature rise of refrigerant vapor above its saturation point after leaving the evaporator, indicating proper refrigerant charge and system balance. Superheat readings between 8-15 degrees Fahrenheit confirm adequate charge; readings outside this range suggest undercharge or metering device problems. This diagnostic uses a combination of saturation pressure and refrigerant temperature measurements.
Technical Details
Technicians measure low-side pressure at the evaporator outlet, convert this pressure to saturation temperature using refrigerant charts, then measure actual refrigerant temperature at the same location. The difference is superheat. For example, if low-side pressure indicates 40 psig saturation temperature of 35°F, but the actual refrigerant temperature is 50°F, superheat equals 15°F. Electronic superheat calculators simplify this process. Some systems target 10°F superheat; others specify 12-15°F depending on expansion device type.
Practical Significance
Proper superheat prevents liquid refrigerant slugging that damages compressors. Low superheat indicates undercharge or evaporator restriction; high superheat suggests overcharge or metering device malfunction. Superheat checks performed during commissioning and annual service ensure consistent system capacity and reliability.