axv question

[nrfd25]

Can anyone tell me how to charge a refrigeration system with a n axv (constant presure valve) the unit is a custom airhandler, condensing unit r22 with reciever and an accumulator also installed. the techs that are installing these units are over charging them, My suggestion was to forget the siteglass and charge by superheat only when desired load temp is within range.

[airworx]

charge by subcooling. subcooling is what tells you the system is charged not superheat. AXV is a non adjustable expansion valve. This is probably a residential or light commercial application and if so the unit should have the design subcooling. You can also call the manufature of the condenser and get the proper subcooling. If not then a good rule of thumb would be anything over 15 degrees subcooling is overcharge. This said I have run across some hhi-efficient heat pumps that were up to 18 degrees.