• SkillCat Team

Refrigerant Oils (Overview)

Updated: Mar 29

EPA 608 Core Chapter 26 (Take full course for free)


In this module, we will introduce how oils are used in HVAC.


1. Purpose of Oils


In HVAC systems, we use refrigerant oils in the compressor. As refrigerant moves through the system, it will carry some of the oil with it. But ideally, most if not all of the oil should be in the compressor.


Recall that in the refrigeration cycle, the compressor’s job is to increase refrigerant pressure. The compressor increases pressure in order to increase the temperature of the refrigerant.


In the compressor, refrigerant oils are used to

  • Lubricate the system

  • Remove excess heat, and

  • Seal the system

The main purpose of refrigerant oils is to lubricate the system. Lubrication helps the components move smoothly in the system, especially as temperature and pressure increase.


In the compressor, refrigerant oils help move heat and contaminants away so it can function properly.


And finally, refrigerant oils help seal the system. It prevents against leaks in the equipment.


2. Oil Sample


If technicians are trying to diagnose what is wrong with a system, they may choose to take a sample of the oil and send it in for testing. Oil samples give you valuable information on what is going on inside the system.


Technicians may want to take an oil sample if they suspect the following culprits:

  • Moisture

  • Acid

  • Oil sludge formation

  • Oil waxing


As we mentioned, moisture can react with oils in the system to degrade the oils. An oil sample will tell you if this is going on in the system.


Recall that acid can break down metal system components, which causes major failures.


Technicians should be especially aware of acid after a compressor burnout. After compressor burnouts, there can be residual acid which will contaminate the oil in the system. Taking an oil sample will confirm if there is acid.


Refrigerant oils can decompose in the system due to a variety of factors, causing the oil to become a sludge. When oil decomposes, it can no longer do its job and causes the system to run inefficiency. An oil sample confirm whether this is happening.


After any major component failure or major leak, you need to take an oil sample. This includes the case of a compressor burnout, which we will talk more about in the next chapter.


4. Conclusion


In this module, we looked at the purpose and properties of refrigerant oils. We also discussed the different types of oils and their applications.



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