How Much Refrigerant Do I Need to Add?

 

 

This is a frequent question, from technicians, after a system is installed in the winter months.  There are a few simple procedures to follow to eliminate a trip back to the customer's home in the spring for a complete startup.  

 

Rheem ships all of their condenser units with enough refrigerant for a 15' line set installation.

 

  • Any length over that needs to have the charge adjusted.....BUT WAIT......There is more to it!
  • Rheem also ships a liquid line filter drier with each outdoor unit.  This also requires a charge adjustment too.....BUT WAIT....There is more!
  • Any 90º or 45º elbows, long radius or short radius, that are used require a charge adjustment too!

 

The chart below outlines the guidelines to follow for any Rheem condensing unit installation manualEquivalent Length For Fittings

 

Calculating Actual Charge

Lets look a common scenario and caluclate how much additional refrigerant is required:

 

  • 3/8" x 3/4" x 35' Lineset
  • Factory Supplied Liquid Line Filter Drier
  • (2) 3/4" Long Radius Elbows

 

Since the unit comes precharged with a 15' lineset, lets subtract that from the 35' lineset.  Now we are working with 20' of line set.  You will add 0.6 oz. per foot additional for the lineset, plus 6oz. for the filter drier, and the long radius elbows add 2.6 additional feet.  

 

  • 22.6 ft x 0.6 = 13.5oz + 6oz. (Liquid Line Drier) = 19.5 oz. of additinal refrigerant.  

 

After seeing this example, one might agree that there are a significant amount of systems that are undercharged in the field.  using this method of weighing in additional charge will get you close to where you need to be.  The other factors are the fan speed set for the tonnage of the condenser, the static pressure of the ductwork is satisfacory, and proper installation procedures were adhered to.