This method of charging is used where the evaporator can be readily seen, such as in manual-defrost units, cycle-defrost units, and most commercial units where evaporator temperature is designed to be below 32°F. In residential frost-free units where the evaporator is covered, removal of the cover would be too time-consuming to use this method.
a. If there is no service valve on the suction line, install one and leave it closed.
b. Remove the evaporator cover. Using this charging method becomes necessary when working on a unit where the charging information is not available, or where an ammeter or a charging cylinder (or a charging scale) is not available.
c. Connect a refrigerant tank to the compound gauge on the manifold and also to the piercing valve as indicated in figure 81.
d. Turn on the unit.
e. Turn on the piercing valve, the gauge manifold, and the refrigerant tank as in figure 81.
f. Keep a hand on the valve of the refrigerant tank while watching the frost pattern appear on the evaporator. Let the refrigerant flow into the system while the unit runs.
g. The frost pattern will appear and advance on the evaporator coil.
Once the frost pattern covers all of the evaporator coil, close the valve on the refrigerant tank, the gauge manifold, and the piercing valve.
h. Remove the hoses from the unit. Put some Teflon tape on the threads of the piercing valve and replace the cap.