Refrigeration cycle, refrigerants, and environmental regulations
Domain 5 tests the vapor-compression cycle, charging indicators, refrigerant safety, and federal environmental rules.
The cycle
The compressor raises refrigerant pressure and temperature. The condenser rejects heat and condenses the refrigerant. The metering device drops pressure and temperature. The evaporator absorbs heat and boils the refrigerant. Superheat is the amount of vapor above saturation at the evaporator outlet; subcooling is the amount of liquid below saturation at the condenser outlet. Superheat protects the compressor; subcooling ensures a solid liquid column at the metering device.
Refrigerants and rules
EPA Section 608 certification is required to service stationary air-conditioning and refrigeration equipment. Knowingly venting refrigerant is prohibited; refrigerant must be recovered, recycled, or reclaimed. Leak repair and recordkeeping requirements apply. R-22 is an HCFC that has been phased out of production and import. R-410A is an HFC blend being phased down under the AIM Act. Lower-GWP alternatives include R-32 and R-454B, which are A2L mildly flammable refrigerants and require charge limits, ventilation, and ignition-source control.
Worked example
Suction line temperature is 55°F and saturated suction temperature is 40°F: superheat = 55 − 40 = 15°F. Liquid line temperature is 95°F and saturated liquid temperature is 110°F: subcooling = 110 − 95 = 15°F. Low superheat suggests overcharge or overfeeding; high superheat suggests undercharge or a restriction. Always compare with the manufacturer's charging chart.
Traps that cost marks
Do not charge by pressure alone, mix refrigerants, vent refrigerant, ignore glide on blends, or treat A2L refrigerants like R-410A without reviewing charge limits.