Given the range of equipment to service or install, it is important to always consult equipment manuals when determining appropriate refrigerant charging methods and amounts. For example, charging methods and calculations for Ductless products will differ from standard residential A/C & H/P equipment.
There are myriad conditions to consider when charging a system during service or installations. The most accurate way to make sure any system has the correct amount of refrigerant is called critical charge. With critical charge it means that there will be a specific weight of refrigerant to be charged.
If line length is beyond 80 ft (24.38 m) or greater than 35 ft (10.7 m) vertical separation, see Long Line Guideline for special charging requirements.
If conditions are favorable, outdoor temperature is between 65° F (18° C) and 100° F (38° C), and the indoor temperature is between 70° F (21°C) and 80° F (27° C), check system charge by subcooling method.
If any adjustment is necessary, adjust charge slowly (no greater than .5 lb per minute) and allow the system to operate for 25 minutes to stabilize before declaring a properly charged system.
During new installations, the outdoor unit contains the correct amount of refrigerant charge for operation. However, additional refrigerant will be needed if a larger tonnage coil is used. For Bryant and Payne residential equipment, adding or removing charge should be calculated using the ratio of .6 oz/ft (17.74 g/m) of 3/8 liquid line above or below 15 ft, respectively.
Ductless systems have a minimum required pipe length that must be achieved. They only require additional refrigerant if and when it exceeds the total maximum piping lengths listed in the literature. Additional refrigerant amount is .16 oz/ft for most applications. Do not exceed the maximum piping lengths or systems will experience failures.
The days of “beer can cold” charging methods have been gone for some time now. Using the proper methods and techniques will ensure equipment performance and make happy customers.