How Much Refrigerant Do I Need to Add?

  • This question is asked quite often from technicians. Usually it is related to an A/C installation that was performed over the winter
  • In an effort to eliminate spending  time having to go back to a customer’s home in late spring or early summer for a startup some simple procedures can be performed.

Rheem ships its condensing units with enough refrigerant for a 15’ line set.

  • Any length over that needs to have the charge adjusted…BUT WAIT…There’s more to it!
  • The factory also ships a liquid line filter drier with each outdoor unit and guess what?, it requires a charge adjustment too…BUT WAIT…There’s more!
  • Any 90° or 45° whether long radius or short radius requires a charge adjustment too …!
  • The charts below are from any Rheem condensing unit installation manual

LIQUID LINE diameter and adjustment p/ft:

Let’s look at a common scenario and calculate how much additional refrigerant is required:

- 3/8 x ¾  x  35 ft lineset

- Factory supplied liquid line filter drier

-2   ¾” long radius elbows

35’ – 15’ = 20’ @ .6 oz p/ft

Filter drier             6 oz.

LR elbows =         2.6 additional ft

So now we have 22.6 ft x .6 = 13.5 oz + 6 oz = 19.5 oz of additional refrigerant

  • After seeing this one example one would agree there are a lot of systems undercharged in the field.
  • Using this method of weighing in additional charge will get you close to where you need to be as long as the fan speed is set for the proper tonnage and static pressure, the duct work is satisfactory and proper installation procedures were adhered to.