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.

Testing a Property’s Building Envelope For Infiltration

Specialized building inspectors utilize a device called a “Blower Door” to assess and aid in the buildings air tightness.

Benefits resulting from an air tight structure include:

  • Reducing energy usage attributed to air leakage.
  • Avoiding humidity or moisture build-up causing water condensation problems.
  • Avoiding unpleasant drafts created by cool air leaking in by way of the outdoor environment.
  • Making certain that the properties air quality is properly ventilated.

How They Work

A “Blower Door” is a strong fan that mounts directly into your exterior doors framework.  The fan draws air out of the building, decreasing the air pressure inside. The greater outdoor air pressure enters the building by means of unsealed crevices and voids in walls, windows and ceilings. The inspectors use a smoke pencil to help discover air flow leaks.  Such assessments verify the air infiltration rate for a building.

“Blower Doors” are constructed of a framework and adaptable section which fit within a doorway.  A variable-speed fan and pressure gauge determine the pressure differences indoors as well as exterior to the property, and an airflow manometer and tubes are used to gauge airflow.

There are two kinds of blower doors: calibrated and uncalibrated. It is essential that auditors make use of calibrated Blower Door Units. This particular type of blower door features numerous gauges which assess the quantity of air drawn out of the building through the fan. Uncalibrated blower doors will simply identify leaks in properties. The uncalibrated units offer no method for analyzing the over-all air tightness of the building. The calibrated blower door’s information permits the inspector to assess the quantity of air leakage as well as the success of any air-sealing work.

Planning for a Blower Door Test

Complete the following measures to get your property ready for a blower door test:

  • Close windows and open up inside doors.
  • Turn down your thermostats for heating units as well as water heating units.
  • Cover ashes in wood stoves and fire places with moist newspapers.
  • Shut fireplace dampers, fireplace doors, and wood stove air intakes.

A Blower Door test and the resulting sealing of the building envelope will return energy savings for years to come.