How to Diognose Non-Condensables

Air, nitrogen, hydrogen and other foreign gasses present in a refrigerant system are referred to as non-condensables since they will not condense into a liquid at pressures encountered in a refrigeration system. These gases will accumulate in the condenser coil and take up valuable condenser coil circuiting.


  • Poor installation skills
  • Failure to properly evacuate the system after the system has been opened


Systems running with non-condensables present will experience higher than required head pressure.  The suction pressure will be low if there is no subcooling present  If subcooling is present, the suction pressure may be slightly high with fixed metering systems and may be normal with TXV systems.

The subcooling level with non-condensables will be lower than required.  If no subcooling is present, there will be flash gas in the liquid line before the metering device.

The superheat level will be high when flash gas is present.  If there is subcooled liquid entering the metering device and the suction pressure is high with a fixed metering system, the superheat may be low.  If the system is using a TXV, the superheat may be normal.

Test the System

  • The system must have a discharge line pressure port to perform this test.
  • Pump the refrigerant into the condenser coil by running the compressor with the liquid service valve closed.  Only pump the system down to 0 PSIG suction pressure.  Never run in a vacuum.
  • Shut off the condensing unit when pump-down is finished.  Disconnect power to the compressor and then call for cooling so that only the condenser fan runs.
  • Measure the temperature of the outdoor air and air leaving the condenser coil.  When they are equal to one another, shut off the condenser fan.
  • Compare the pressure in the condenser coil to the temperature of the outdoor air.  The pressure you read should equal the pressure at the saturation temperature equal to the outdoor air temperature.  If the pressure is higher than it should be, non-condensables are present.  If non-condensables are present, recover the refrigerant and recharge.