Cooling Equipment, Refrigerants, and Charging Procedures
This domain tests equipment ratings, refrigerant handling, and the charging method that matches the metering device.
Equipment and ratings
- SEER2 and EER2 replaced SEER and EER; capacity at design conditions comes from the AHRI matched combination, not the outdoor unit alone.
- Airflow runs about 350 to 450 CFM per ton; a healthy air temperature split is roughly 16 to 22 F.
Refrigerants
- R-410A is a near-azeotropic blend with small but real glide; it is charged as a liquid from the cylinder.
- R-32 and R-454B are A2L mildly flammable refrigerants. Nameplate charge limits, ignition sources, and leak detection requirements come from the mechanical code.
- Recover, recycle, and evacuate per EPA Section 608. Never vent.
Charging by method
- TXV or EEV: charge to the subcooling target on the nameplate.
- Fixed orifice or piston: charge to the superheat target from the manufacturer chart, using indoor wet bulb and outdoor dry bulb.
- Weigh in the charge when line length exceeds the factory charge, using the per-foot correction.
- Evacuate to 500 microns and confirm a decay test before releasing charge.
Worked example
Nameplate target is 10 F subcooling. Liquid pressure is 410 psig on R-410A, about 119 F saturation. Target liquid-line temperature is 119 - 10 = 109 F. Measured liquid-line temperature is 115 F, so subcooling is 119 - 115 = 4 F. The system is undercharged; verify airflow and check for leaks, then add liquid refrigerant and recheck.
Traps that cost marks
- Charging a TXV system to a superheat target.
- Vapor-charging a blend and fractionating the cylinder.
- Adding refrigerant before checking airflow; low airflow mimics an undercharge with high superheat and low suction pressure.
- Using an R-22 PT chart on an R-410A system.