Charging Procedures
Liquid-only charging requirement for R-410A, weigh-in charging method, subcooling charging for TXV systems, and proper techniques to prevent fractionation and system damage.
- Explain why R-410A must be charged as liquid, not vapor
- Perform weigh-in charging using a refrigerant scale and manufacturer's specified charge
- Charge a TXV system to the correct subcooling target
- Describe how fractionation occurs and its effect on system performance
Lesson 1
Why R-410A Must Be Charged as Liquid
The Fractionation Problem
R-410A is a blend of R-32 (50%) and R-125 (50%). Although it behaves nearly like a pure refrigerant during normal operation, the two components have different boiling points. R-32 boils at -62 degrees F and R-125 boils at -55 degrees F. If you charge R-410A as vapor from a cylinder, the more volatile component (R-32) evaporates preferentially, and the vapor entering the system has a higher concentration of R-32 than the 50/50 blend ratio.
This process is called fractionation. The result is that the system receives a blend with the wrong composition, and the liquid remaining in the cylinder also has the wrong composition. Neither the charged system nor the remaining cylinder contents are true R-410A.
Liquid Charging Is Not Optional
R-410A must always be charged as liquid. This means the cylinder must be inverted (if it does not have a dip tube) or the cylinder valve's liquid port must be used. Charging R-410A as vapor causes fractionation that alters system pressures, reduces capacity, and can damage the compressor.
How to Charge Liquid Safely
Charging liquid refrigerant directly into the low side of a running system risks sending liquid into the compressor, which causes liquid slugging. There are two safe methods:
Method 1 - Liquid into the high side (system off): With the system shut down, connect to the liquid line service valve (or high-side port) and allow liquid to flow from the cylinder into the system by pressure differential. This is the fastest method for initial charging but requires the system to be off.
Method 2 - Metered liquid into the low side (system running): Use a metering device on the charging hose (a restrictor or the gauge manifold valve cracked open slightly) to flash the liquid into vapor before it enters the suction line. This allows you to charge while the system runs, but you must meter the flow carefully to prevent liquid from reaching the compressor.
R-410A must always be charged as liquid to prevent fractionation. Invert the cylinder or use the liquid port. When charging liquid into the low side of a running system, meter the flow through a restrictor to flash it to vapor before it reaches the compressor.