How to Determine an Overcharged Unit with a TXV

  July 30, 2018      Jeff Rosenblum


This quarter’s Tech Tip is brought to you by Allied Air.

When a unit is slightly overcharged with a TXV metering device, both suction and superheat may appear normal but the performance and efficiency are diminished. These conditions are caused by the TXV as it meters refrigerant flow into the evaporator and excess charge is stored in the condenser. If excess charge levels are extremely high, this elevates the head pressure and liquid sub-cooling levels. If the charge is high enough, the suction pressure may be high with low superheat present.
When charging R-410A systems, always charge as a liquid and follow the procedure below:
•  Operate unit a minimum of 10 minutes before checking charge..
•  Measure liquid service valve pressure by attaching an accurate gage to service port.
Measure liquid line temperature by attaching an accurate thermistor type or electronic thermometer to liquid line near outdoor coil.
•  Calculate subcooling (saturation temperature—measured temperature) and compare to table on back of control box cover
•  Add refrigerant if subcooling is lower than range shown in table. Recover refrigerant to decrease subcooling.
 If ambient temperature is lower than 65°F, weigh refrigerant according to the nameplate data.

As always, if you need assistance with charging please feel free to contact the Famous Supply Technical Services Department.

Jeff Rosenblum 
Technical Support
19 Years Industry Experience
Cell (330) 962-2491
[email protected]