Determining the Correct System Charge Weight

Charging by weight is used if a complete charge is to be added to the system and the weight of the charge is known. To find the needed charge weight and type of refrigerant, check the equipment nameplate (SP-4-5), or the manufacturer’s service literature.

Nameplates on residential split systems normally give the charge weight for the system based on the use of a standard refrigerant line length. Always be sure to consult the manufacturer’s service literature to find out what the specific standard line length is. If the system being serviced uses a line length that exceeds the standard line length, consult the manufacturer’s instructions to find the amount of additional refrigerant charge that must be added to compensate for this increased length.

For example, assume the nameplate charge weight for a residential split system is marked “5 pounds” based on a standard line length of 15 feet. Also, assume that the system is using a line length of 35 feet. Further, suppose that the manufacturer’s instructions require .58 ounce of additional refrigerant for each foot of 3/8-inch liquid line in excess of 15 feet. Based on this information, you would charge the system to 5 pounds and 11.6 ounces (5 pounds nameplate weight + 20 feet excess length x .58 ounce per foot).

If adding a filter-drier or other accessory, also be sure to compensate for its volume by adding the amount of charge as stated in the manufacturer’s instructions.

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