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Checking for refrigerant contamination

By Richard Hawkins, MACS Contributor

Over the past several weeks we have focused on the issues caused by refrigerant contamination both in vehicles and in recovery/recycling equipment.  This has illustrated the importance of refrigerant identifiers.  A large percentage of MACS members have refrigerant identifiers and use of them on vehicles that come into their shop for A/C service prior to beginning any service work is standard procedure.

However, there are a lot of non-MACS member shops who do not have identifiers and unfortunately are not aware of the potential issues which can be caused by refrigerant contamination.

Tech Line Call

I have witnessed this first-hand with tech calls. When it was encountered, the conversation would go something like this:

Me:  Based on the information you have supplied; it sounds like there is a very high probability the refrigerant in that vehicle is contaminated.

Technician:  Contaminated with what?

Me:  Either air or another refrigerant or perhaps both.  Do you have a refrigerant identifier?

Technician:  No, I don’t.  (Unfortunately, sometimes the answer might also be something like: What do you mean? This of course indicated unfamiliarity with refrigerant identifiers.)

Me:  Would you happen to know of another shop that has an identifier that you might be able to take the car over to and test it?

Technician:  No, I don’t.

Me:  OK, there is another way you can determine if the refrigerant is contaminated but it is much more involved than just connecting a refrigerant identifier and pushing a button.  Also, it isn’t going to tell you what the contaminate is.

At that point I would explain the procedure, so we will examine it.  It involves conducting a non condensable gas check on a vehicle instead of on a tank of refrigerant. 

For reference purposes, here is a review on conducting a non condensable gas check on a tank of refrigerant.

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 (some R/R/R machines have built-in ones).
  • To obtain the refrigerant liquid temperature, measure the temperature of the lower one-half of the refrigerant container’s outer surface (make sure the thermometer is in contact with the “liquid zone” of the tank). Using only the air temperature reading in the vicinity of the refrigerant container can result in incorrect information.
  • Compare the pressure gauge and temperature readings with the limits found in Tables 1 and 2. Use the figures in Table 1 for CFC-12, and the figures in Table 2 for HFC-134a.
  • If tank pressure is equal to or below the figure listed in the table, the refrigerant does not contain an excessive amount of air.   See figure #1. 

Figure #1:  Maximum allowable container pressures  

  •  If tank pressure is higher than that listed in the table for the ambient temperature, it is advisable to use a refrigerant identifier and confirm if the high pressure is due to excess air or cross-contamination.
  • Remember: The information in the tables is only reliable if the tank has been kept at a stable temperature for several hours before the readings are taken, has been kept out of direct sunlight, contains some liquid refrigerant, and no refrigerant cross-contamination exists. It is also important that during the purge process, the tank does not become cold, since a cold tank of refrigerant will reflect an incorrect pressure reading. Also keep in mind that while pressures higher than those in the charts indicate contamination, they do not indicate the type of contamination (is it air, mixed refrigerants, or a combination of both?).

Now let’s apply this to checking for contamination in a system instead of a refrigerant tank.  The big difference in conducting this test on a tank of refrigerant verses a vehicle is that the system in a vehicle has components which are spread out under the hood and there is an evaporator (or evaporators) located inside of the vehicle.  This makes it more challenging to get the temperature of all the components the same and the temperature must be the same for the test to be accurate.

To conduct this test the vehicle should be placed in a room with a temperature of at least 65° F for a period of 12 hours with the windows down, protected from direct sunlight.  Check the temperature of several A/C components under the hood. Record the temperature.  Now check the temperature of the dashboard inside the vehicle (this should provide a good indication of what the evaporator temperature is) and compare it to the temperature of the A/C components under the hood.  If the temperatures are not the same, then the vehicle must be left in the room longer for the temperatures to equalize.

If the temperatures are the same, then install a calibrated pressure gauge on a service port.  Compare the pressure gauge and temperature readings with the limits found in the table provided in figure #1.  If the pressure reading is equal to or lower than that listed in the table for the ambient temperature, then that indicates refrigerant is not contaminated.  As a result, it is safe to recover it if necessary.

If the pressure is higher than that listed in the table for the ambient temperature, that indicates the refrigerant is contaminated. Do not recover the refrigerant with your machine that you use for regular service because at this point (without a refrigerant identifier) it is not possible to know whether the contamination is due to the presence of air or another refrigerant.

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