Jim Wheeler: Refrigerant oil or lubricant?
“All oils are lubricants, but not all lubricants are oil.”
Back in the late 1900s there was just refrigeration oil and the only differences were the viscosity. However, with the advent of non-chlorinated refrigerants, we now have non-oil-based “lubricants” that are being used in place of refrigerant oils and service techs that enter your shops don’t always understand which type they need (they’re not chemists).
Oils usually come from plants or animals and most of the older refrigerant oils come from crude oil — plant- or animal-based oils that have been sitting under the ground for thousands of years. Chemically, they are made up of long strings of hydrogen, oxygen and carbon atoms so complex that they get tangled up with each other and stick to each other, which is called “viscosity.” And the more complex the molecular chain, the higher the viscosity.
But new refrigerants require new types of lubricants. Why?
Understand that most compressors have friction-contact surfaces that will overheat and wear out if they are not lubricated, so they must have some means of distributing the lubricant to the wear surfaces. However, with every rotation of the compressor, a fine spray of lubricant is lost into the closed-circuit system. And if there isn’t some means to carry it back to the sump, the compressor sump will go dry and the moving parts will overheat and lock up. Therefore, the lubricants have to be compatible with the refrigerants in the closed system so they can be returned to the compressor by the refrigerant.
Chlorine-based refrigerants such as R11, R12 and R22 are miscible (mixable) with oils. However, nonchlorinated refrigerants such as R123 and R134a are not miscible with oils, so they require a different type of lubricating chemical. Therefore, if you put regular refrigerant oil in a compressor that is pumping a nonchlorinated refrigerant, the compressor will eventually lock up due to a lack of lubricant. Also, if you put modern lubricants in a system that uses chlorinated refrigerants, the compressor also will eventually lock up.
It helps to understand that too much oil or lubricant circulating in the system decreases its cooling or heating efficiency because its viscosity causes the lubricant to stick to the coil surfaces, which impedes the thermal transfer of the refrigerant. And where a technician adds too much lubricant to the compressor (I’ve seen this happen), it takes the place of the refrigerant and cooling (or heating as with heat pumps) is greatly reduced.
Currently there are two types of new compressor designs that use little lubricant, which makes these systems operate more efficiently, and we may soon see such ideas become integrated into all compressors as technology continues to advance. One of these compressors used on centrifugals has magnetic bearings, so there is no bearing-surface contact that needs lubrication. The other is operated by little more than a vibrating disk and it is being used on domestic refrigerator compressors.
Of course, you can’t change the lubricants or even check their level in “hermetic” (welded steel) compressors. So, better technicians will seldom purchase lubricants for use in these types of systems. However, the lubricants can be checked and even changed in serviceable hermetic compressors (large compressors that can be opened for servicing). This is why you stock lubricants on the shelves. Remember, older systems that use CFC or HCFC refrigerants use oils and newer nonchlorinated systems use the new lubricants.
I leave you with a Q&A. Why would someone wish to remove and replace the lubricant in a compressor?
It has become contaminated by poor installation or servicing techniques.
They are upgrading the refrigerant to a nonchlorinated type.