Ester Oils

Question: I have come questions concerning the new ester oils that are already on the market.

There is a lot of talk about the ability of the oil to retain water vapor. How do you get the moisture out of the oil once it is in there? Is the process different after the oil is in the system? How do you know when the oil is dry?

Will the moisture still cause freeze-up inside the thermostatic expansion valve on low temperature systems, or can it remain in the oil unit overheated to cause the oil to break down?

Does it change the Micron reading from 1,000 Microns that a deep vacuum will rise to when a shut-in is performed on a wet system?

-Roy Hermanski, Pampa, TX

Answer: Perhaps the best approach in answering this series of questions is to first assure ourselves that moisture continues to be material or substance that we do not want in a refrigeration system. A service technician must continue to be vigilant in the use of the appropriate techniques and service tools (i.e. driers) toward minimizing the presence of moisture in such systems.

Today, however this task has been heightened with the advent of polyol ester lubricants. These lubricants have been found to be the best choice when using an HFC refrigerant, as they are very compatible with and exhibit excellent low temperature characteristics when used with HFCs. Moreover, the polyol esters are also very compatible and miscible with CFCs, HCFCs, and other oils, making them ideal for retrofitting. They do have one drawback, a manageable one but a drawback nonetheless. They are hygroscopic, having the ability or affinity to absorb moisture.

The hygroscopic characteristic of these oils, however, does not change your techniques or procedures; it simply requires you to be more persistent in practicing them. You use the same tools, such as driers and moisture indicators, to manage the situation. And, you use conscientious techniques, such as keeping the oil containers tightly capped at all times, to minimize, if not eliminate moisture ingress into the oil or the system.

Because of the polyol ester oil's affinity for moisture, the moisture will tend to stay as part of the oil, assimilated by the oil rather than being free or separate from the oil as it is in a traditional mineral oil system. However, this “affinity” will not preclude or prevent you from removing the moisture as discussed above or with a vacuum pump.

-John Lawler, Nu-Calgon