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Mobile A/C Refrigerant Contamination


Whenever you hear the term refrigerant contamination the first thing you probably think of is mixed refrigerants. However, the most prevalent contaminant, particularly in recycled refrigerant, is air.
What problems are caused by excess air in a vehicle air conditioning system?
Air, in excess of allowable amounts, can cause the system to operate at pressures that are higher than normal. This can result in noisy system operation and loss of air conditioning performance. (Air is not a good heat transfer medium, as refrigerant and higher pressures also mean higher condenser temperatures, which can also degrade system performance.)
It can also cause the system’s high pressure compressor clutch cut out switch to inhibit compressor clutch operation, and/or depending on the circumstance, possibly cause damage to system components due to overpressure conditions. In systems that use the low side pressure to control the evaporator (such as pressure cycling or variable displacement compressors) a system having excess air in the refrigerant will have a loss of performance.
Generally speaking, having more than about 2% air (by weight) in the refrigerant charge can start to cause problems with system operation. With some systems, every percentage point that air contamination exceeds 2% can lead to a one degree F increase in evaporator outlet temperature. For example, a system containing 10% air may be blowing eight degrees warmer than it should at the dash outlets, even if everything else in the system is functioning perfectly.
The bottom line is that the maximum acceptable amount of air contamination is generally considered to be no more than 2%.
How can technicians determine if refrigerant contains too much air?
The only way to determine the amount of air contained in refrigerant is to use a refrigerant identifier. To determine if a container of refrigerant has excess air, the following approach can be used.
The container must be kept at a stable temperature for several hours before taking the readings. In a busy shop atmosphere, this is not always possible.
Contamination can also be caused by mixed refrigerants. In other words, the pressure/temperature method cannot identify whether the higher readings are being caused by air in the refrigerant, or if they are being caused due to refrigerant cross contamination.
Pressure/Temperature Method for Determining the Amount of Air Contained Within Refrigerant in a Container
To determine if a tank of recycled refrigerant contains an excessive amount of air, the tank must be stored at a temperature of at least 65° F for a period of 12 hours, protected from direct sunlight. It is also advisable not to store tanks directly on the cement shop floor since the floor temperature can affect the tank temperature. Placing some form of insulation, such as a piece of wood between the tank and the floor will help stabilize the tank pressure. If these conditions have been met, a check for air may be performed as follows:
Install a calibrated pressure gauge to the refrigerant container. The gauge should be graduated in 1 psi divisions.
When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.
You can E-mail us at or visit to find a Mobile Air Conditioning Society repair shop in your area. Visit to find out more about your car’s mobile A/C and engine cooling system.

3 responses to “Mobile A/C Refrigerant Contamination”

  1. Karl Matis says:

    “A/C Sytem Contamination” is the title, yet the text makes me think it should have been titled “A/C Refrigerant Contamination; good info no less. But if we are going to address “A/C System Contamination”, let’s not overlook the more prevalent system contamination problems of wrong oil, burnt oil, excessive oil, excessive dye, leak sealer, seal sweller, moisture, and metal debris.

  2. Yes, Karl those other contaminants are on the agenda! If you’d like to send any blog contributions we’d love to have them. Thanks for taking the time to read the blog and reply. —Marion

  3. jeff says:

    Great info. Please tell me what percent by weight means. If a r134 system hold 2.10 lbs what would 2.1% mean in % by weight? Is it still just 2.1% of air in the system? Thanks