Refrigerant Charge for a Heat Pump or Air Conditioner

To purchase and use most refrigerants, you must hold an EPA Certification.  It is illegal and there are significant fines for handling refrigerants without the certification.

Heat pumps are air conditioners and need to be charged in the cooling season with an outside temperature above 70 degrees F.  Follow the manufacturer’s directions, usually on a label attached to the inside of the service panel.  The standard charge may be stamped on the model/serial label.  If the system is a split system, additional refrigerant for the line set piping is required.

Methods used to adjust the refrigerant charge:

  • All systems… Weigh-in the charge.  Remove all refrigerant and replace it with an accurate charge using scales or charging cylinder.
  • Systems with fixed orifice.  Measure superheat and add/remove refrigerant to obtain the target superheat.
  • Systems with TXV (thermal expansion valves).  Measure sub cooling and add/remove refrigerant to obtain the target sub cooling for the system.  (adjust the TXV for proper superheat)
  • Approach method (Lennox) See charging by the approach method on this site.
  • Beer Can Method.  Not recommended but very common.  Your energy consumption can double and system capacity can be reduced by 50% using this method.  You add/remove refrigerant until the suction line is as cold as a beer can.  We like 33F beer in Texas.

Superheat … degrees F added to the saturation temperature (temperature/pressure that the refrigerant changes from a liquid to a gas) of the refrigerant in the suction line as measured by the pressure.  A pressure gauge and digital thermometer are required to measure and calculate superheat.  Digital gauge sets are available that will do the calculations.  10F to 13F superheat is typical but follow manufacturer’s recommendations.

Sub cooling.. degrees F subtracted from the saturation temperature in the liquid line leaving the condenser and before the expansion device.  9F to 13F is typical but follow manufacturer’s recommendations.