Choosing HVAC Compressor Oil for Your Equipment

Indeed, knowledge is power. HVAC compressor oil is an essential part of any air conditioning system. Having the correct information on how to choose the right HVAC compressor oil helps one to save a lot in monetary terms and on maintenance as well. The type of oil you want to use depends on its viscosity. The oil’s thickness level shows its ability to withstand the shear stress when the machine is running.

Choose the oil that brings a good cooling effect to the machine. The oil should have excellent dielectric strength so that it would not interfere with the normal functioning of the compressor. First-time air conditioner users find it hard to choose the right oil from the market flooded with many oil brands. Due to this reason, the users are easily swayed into buying any oil that may turn out to be harmful to the air conditioning system.

It is essential to read the manual or consult the manufacturer on the right oil to use to get a relive from the fear of spoiling the system with the wrong oil. It should not have a high moisture content, as this would affect the system’s performance. Your system needs quality oil to give you quality service as well so serve it well with the right oil, and it will give excellent service back!

Compressor Oil Properties


Viscosity is the way of measuring the thickness of the oil which informs us of its ability to resist shearing stress. One of the units of measurement of viscosity is Saybolt Seconds Universal (SSU). This is achieved by putting the oil sample on the standard equipment at a preset temperature with a standardized orifice and allowing it to flow. The time taken for this to flow is saved. The bigger the viscosity number, the thicker is the oil as well as the slower it flows.

The measurement unit for viscosity is poise. Almost all the oil measured is under 1 poise therefore, the smaller scale called 1/100 poise or centipoise is often used.

Generally, a larger compressor with bigger gaps and parts needs thicker oil for productive functioning of your equipment.

Chemical Stability

While using the compressor oil, always stick to the compressor manufacturers suggested oil as some oil may interact with the refrigerant found in the machine. If the chemical reaction happens, sludge, carbon, and acids may be formed that will affect the efficiency and lifetime of your compressor.

Dielectric Strength & Moisture

Compressor OilAs the compressor oil used in a hermetic compressor is often exposed to the coil of the motor, it’s really important that it has very good dielectric strength. The bigger the dielectric strength, the more suitable the electrical insulating value of the oil.

Nearly all oils will dissolve a lot of moisture and water which makes them undesirable. When water is in the refrigerant, ice will form if the temperature goes below zero degrees and caused issues for the expansion valve.

Copper plating may take place with the presence of refrigerant, oil plus moisture in the system. Moisture within the oil also resulted in the dielectric strength of the oil to get reduced considerably as water is a pretty good conductor. Hence, as long as possible, try and cut the level of moisture in contact with the compressor oil.

Typical Compressor Oil & Refrigerants

The two varieties of oils widely used in the compressors are synthetic oils or mineral.

One type of mineral oil (MO) known as Naphthenic which is commonly used in lots of equipment.

Synthetic oils like esters, glycols, and alkylbenzenes (AB) are actually used in the refrigeration programs for a while with no problem.

CFC refrigerants like R115, R114, R113, R13, and R12 are using alkylbenzene or mineral oil as their lubricants. Likewise, HCFC refrigerants like R409A, R401A, R22, and R123 are usually using these lubricants into their design.

Recently HCFC and CFC refrigerant usage started to decrease because of their ozone-unfriendly properties. The use of new HFC refrigerants like R134a, R23, R32, R407A, R410A, and R407C have raised in HVAC equipment. These latest refrigerants use POE(Polyol esters) as a lubricant.

One drawback of Polyol esters is it absorbs moisture often more as opposed to mineral-based oils. Hence correct ways should be used when handling this compressor oil to cut the contact of the oil with the environment. Metal containers are recommended in place of plastic containers to avoid moisture from entering into the containers.


When repairing the compressor, always check with the manufacturers of the compressor to learn the type and amount of oil you can use for that specific refrigerant.

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