Ester Oils

Question: On the container of an ester-based oil for use with R-134a, it states that once you open the container and use the amount needed, you should get rid of the remaining oil because of the moisture that is absorbed by the oil when the container is open.

So this means that as expensive as this oil is and even though it only comes in gallon containers, you could use just 6 to 10 oz. and have to throw the rest away.

I don't think this is right. I think they should sell the product in smaller containers.

-Cloduardo Bernard, Middletown, NY

Answer: In answer to your question, no, you do not need to necessarily discard any remaining ester once you have opened the container and used what you need. So long as you cap the container tightly after each use, being careful and exercising cleanliness as well as acceptable procedures in obtaining the oil from the bottle, you may retain the oil and use it as needed on another job.

Because the polyol esters are more hygroscopic than the mineral oils and alkylbenzene oils that we've been using for many years – hygroscopic being the ability to absorb moisture – manufacturers, packagers, and marketers of these oils have taken great pains and gone to great lengths to caution the users about this characteristic. We all want to avoid the possibility of moisture entering a system, and sometimes the advice or directions toward this end can be a little overzealous. The “direction” you question would be an example of this.

In addition, most brands of polyol esters today are available in smaller packages (i.e. quarts) to help the service technicians obtain the optimum package size for immediate intended use or needs. Metal construction of containers is also used, and this provides even more protection. Finally, don't become overly alarmed that, during the course of servicing a system of after repeated uses of a bottle of polyol ester, a small amount of moisture (1 or 2 to 10 ppm) may enter the system. So long as the proper service procedures are exercised, this amount of moisture will be minimized. Moreover, the proper use and application of the correct driers will remove the moisture.

-John Lawler, Nu-Calgon