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.

What Size Air Conditioner Do I Need For a 3000 Square Foot House?

One of the questions most often ask is what size air conditioner do I need to heat cool a 3000 square foot house?  The problem is you are asking the wrong question.  The question should be how much heat gets into my 3000 square foot house that the AC System must remove. 

We could tell you that the average home needs one ton of air conditioning for each 500 square feet of conditioned space and we could tell you that the average man wears a size 7¼ hat.  If you buy yourself a 7¼ hat without measuring, it will probably be the wrong size.

Heat does enter the building through walls and ceilings, so there is a relationship between AC size and square feet.  The amount of heat entering through the ceiling and other building envelope components is highly variable depending on factors such as the amount of insulation in the attic. 

There are many sources of heat that must be measured or estimated to determine the AC System size.  They include: walls, ceilings, windows, floors, doors, air leaks as well as internal heat such as people and kitchen appliances. 

Other factors are also important to calculate heat gain such as the outdoor temperature on the hottest days and the temperature you want your AC System to maintain indoors on those days.

You can hire an engineer to measure and calculate heat gain for sizing an air conditioner or heating system and many HVAC Companies will provide this service for no charge.  There is no reason to guess.  See this article for additional information

Finding The Right Heat and Cool Air Conditioner

Consumer reports does not rank or review central heat and cool air conditioners.  The quality of the instalation far overshadows any minor differences in brands.  Selecting an air conditioner should focus on selecting an air conditioning contractor experienced with your specific needs and requirements. 

Select an air conditioning contractor based on their market specialization:

• Appliance Retailers sell and service room and window units.
• Residential Service Contractors have technicians skilled in service and replacement in occupied homes.
• Commercial Service Contractors have technicians skilled in the wide variety of commercial equipment diagnostics and repair.
• Residential New Construction A/C Contractors have the technicians that can hit a construction site and rough-in a new system in a hurry without having to worry about furniture or occupants.
• Mechanical Contractors have new construction crews skilled in efficiently installing ducts and pipes, for ground-up or unoccupied construction.

Using a residential new construction crew in an existing occupied home to install heat and cool equipment, seldom results in a happy customer or profitable install.


Most heat and cool air conditioner equipment, in the low to mid-range efficiencies, are pretty much the same.  Many manufacturers use common components.

The more advance high efficiency heat and cool air conditioner could include some exclusive features and benefits.

Ask Questions and evaluate the answers you get.

Before you buy A/C services study your system and become a knowledgeable consumer.  What type air conditioner system do you have?  What do you like and not like about your system, comfort and energy bill.

Solid State AC Unit 175% more efficient. No compressor, no freon.

Solid State AC Unit.   175% more efficient.  No compressor, no freon.

Certificate For ARI Certified Performance

Before purchasing an HVAC air conditioning / heating split system you should have your contractor download an ARI certified performance certificate from the ARI website.  You can have your contractor do this while he is making his in home presentation.  Split systems must be properly matched to deliver the promised efficiency and cooling / heating capacity.

The ARI Directory of Certified Product Performance allows anyone to quickly access information, such as the ability to properly match outdoor condensing units and indoor coils. In addition, the ARI Directory allows a contractor to print out a certificate stating that the installed system is properly matched, thereby protecting the consumer’s warranty

According the ARI, the Directory also includes certified performance information for products covered under their 22 certification programs and acts as the definitive source of information about the performance of ARI certified products.

Sustainability Calculator, Individual Emissions

In the home daily activities cause emissions of greenhouse gases. Individuals can produce greenhouse gas emissions directly by burning oil or gas for home heating or indirectly by using electricity generated from fossil fuel burning.

Within the United States, per person emissions can vary depending on a person’s location, habits and personal choices. For example, the types of fuel used to generate the electricity a person uses can lead to different levels of emissions. A power plant run on coal emits more greenhouse gases per unit of electricity than a power plant that uses natural gas. How much you drive and your vehicle’s fuel efficiency, as well as time spent idling in traffic, also affect the level of emissions. In addition, the amount of recycling done by a person in his or her home can affect emissions by reducing the amount of methane-generating waste sent to landfills.

Your Emissions

Through actions at home, at work, and on the road, individuals can affect their greenhouse gas emissions levels. The first step in reducing your greenhouse gas emissions is to identify how much your household emits. If you have old copies of energy bills, EPA’s personal greenhouse gas emissions calculator can help estimate your household’s annual emissions.

Oversized Furnace Not Detrimental to Efficiency

Oversizing or undersizing the air conditioning systems is critical, but there is no evidence that an oversize furnace is detrimental to efficiency. Further, oversizing a furnace can compensate for duct design and installation issues. Of course, that’s not a good reason to settle for sloppy workmanship and oversizing furnaces.

Heating systems use lower air flow than cooling systems.  Many times furnaces are oversized to provide additional air flow for the cooling system.

The take away is that it is not worth the investment to replace an oversized furnace in an existing home.