Something that can be confusing to a lot of technicians rather they are a residential tech, commercial tech, or a mechanic is refrigerant oil. The goal of a refrigerant lubricant is to lubricate the compressor and to also have the appropriate miscibility and solubility characteristics to interact with the refrigerant accordingly. There are many different types of oil that are used in the refrigeration cycle and it all depends mostly on two things:
- What kind of refrigerant you are working with.
- What the manufacturer of the compressor calls for.
But, what are the different kinds of oils out there? How do they differ? Is there one that is better over the other? Let’s take some time and find out.
Mineral refrigerant oil, also known as Alkyl Benzene oil, is probably the one that most of you are used to. (Please note that while Alkyl Benzene oil can be used as a replacement in most mineral oil applications these two oils are not the exact same. Alkyl Benzene oil is synthetic whereas mineral oil is not.) Until recently mineral oils were the default lubricant used in refrigeration systems. Chances are that if you have an older R-22 unit installed that it is most likely using mineral oil. These types of oils have been used in refrigeration for decades.
When HFC refrigerants began to gain popularity the use of mineral oils started to decline. HFC units could not use mineral oils due to them proving insufficient lubrication and due to the mixing ability of mineral oils.
Refrigerants that commonly used mineral oils were your CFC and HCFC refrigerants such as R-12, R-22, and R-502. Mineral oils can also be used with other refrigerants such as Ammonia or some Hydrocarbons as well.
POE Oil, or Poly Olester Oil, is a synthetic oil that was designed to meet the needs of the changing refrigeration industry. While these synthetic oils have been around for decades they were always seen as too expensive when it came to using in CFC or HCFC systems. This all changed when the phase out of CFC/HCFC refrigerants began in the 1990’s and 2000’s.
HFC refrigerants on the market today are the primary users of POE oil. These can include some of your most common refrigerants such as R-404A and R-410A. As mentioned in our mineral oil section the POE oil was selected for HFC usage to achieve acceptable miscibility between the refrigerant and the oil and also to provide sufficient lubrication to the compressor. In some instances there are some HFC refrigerants and compressors out there that were designed as drop-in replacements for older HCFC units. In these cases using mineral oils may be acceptable but again always check with the compressor and the refrigerant to ensure accuracy.
One last point of note is that POE oils absorb moisture at a much faster rate than mineral oil. Because of this the time allowed for the compressor to be exposed to the atmosphere is much much shorter than what you may be used to for R-22. Best practice is to ensure everything is set and ready before pulling the plugs on the compressor.
PAG oil, or Polyalkylene Glycol, is a fully synthetic hygroscopic oil specifically designed for automotive air conditioner compressors. It is used in R-134a air conditioning systems to lubricate the compressor. When looking at PAG oil you will notice various numbers such as PAG46 or PAG100. These numbers refer to the viscosity of the oil, similar to 10W30 oil. In order to determine the correct PAG viscosity for your vehicle you will need to look up the specifications of your make and model of your vehicle either online or in the instruction manual.
As I stated above the primary users of PAG oil are automotive applications. Since the entire automotive market is switching soon over to the HFO 1234yf I would like to also point out that YF refrigerant also takes PAG oil as well.
Lastly, just like POE oils PAG oils are hygroscopic and can absorb moisture at a much faster rate than mineral oil. Because of this the time allowed for the compressor to be exposed to the atmosphere has to be short. Best practice is to ensure everything is set and ready before pulling the plugs on the compressor. Remember, one of the leading causes of failures in automotive HVAC is contamination.
Regardless of what I have said above the safest method for when choosing an oil to use in your refrigeration unit is to follow the instructions on the compressor. Most of the time new compressors will come prefilled with oil but if they are not or you need to add oil to your system then please please use what the compressor calls for. Otherwise, you could be looking at the wrong oil not circulating through the system and accumulating in your evaporator. This could eventually cause failure of the compressor and other components due to little or no lubrication.
Lastly, some companies have stated that it is ok to mix oils like Mineral with POE but from what I have found in my research the best advice is to NOT mix oils. In some instances the mixed oil doesn’t flow correctly and you could end up with the same result as before of having it pile up in your evaporator instead of circulating and again potentially causing damage to the system.
Thanks for reading and I hope that I was able to answer your questions. As always if you see something that I missed or something that is incorrect please reach out to me by clicking this link.