In routine refrigeration maintenance, refrigerant charging is the most basic yet error-prone step. For blends such as R404A, R407C, R410A and R507, subtle differences in method can directly affect system performance and life.

Why blends cannot be vapor-charged

A blended refrigerant is formulated from two or more components in a specific mass ratio, and the components have different boiling points. Inside the cylinder, the lower-boiling component vaporizes more easily and enriches in the vapor space. Drawing gas from the valve actually extracts a vapor-rich mixture, and the remaining liquid composition deviates from the design value.

This is called composition segregation. After repeated vapor charging, the system composition can differ greatly from the nominal value, directly causing capacity loss, abnormal discharge temperature rise and severe efficiency degradation, and in serious cases compressor overheating damage.

Correct liquid charging method

Liquid charging requires inverting the cylinder (or keeping a siphon-tube cylinder upright) so that only liquid refrigerant is drawn, ensuring the composition entering the system matches the nominal formula. Charge from the high-side liquid line; if charging from the low side, control flow through an expansion device to avoid liquid slugging the compressor.

Five common mistakes

  • Mistake 1: Topping up after a leak. Blend components escape at different rates, so the remaining composition has changed; recover all and recharge the whole cylinder
  • Mistake 2: Insufficient evacuation. Residual moisture reacts with oil to form acid, corroding piping and causing ice blockage; reach -0.1 MPa and verify with a hold test
  • Mistake 3: Not changing the drier filter. The old core after retrofit has absorbed much moisture and impurity and will keep contaminating the system
  • Mistake 4: Mixing lubricants. HFC refrigerants require POE ester oil; mixing with mineral oil causes lubrication failure and oil-line blockage
  • Mistake 5: Estimating charge by experience. Liquid densities differ greatly by refrigerant; charge by electronic scale and verify with superheat/subcooling

How to verify the charge

After quantitative charging, run at rated conditions for at least 15 minutes and measure suction superheat and condensation subcooling. High superheat usually means undercharge; high subcooling may mean overcharge. Through the sight glass, a continuous stream without bubbles indicates normal state.

If you encounter difficult field conditions, please contact the Kaierwen technical support team; our engineers can provide remote diagnosis and on-site guidance.