• SkillCat Team

Refrigerant Oils Properties

Updated: 2 days ago

EPA 608 Core Chapter 2 (Take full course for free)


In this module, we will discuss the purpose of refrigerant oils and also go through their properties. Skip to quiz!


1. Properties


The main purpose of refrigerant oils is to lubricate the system.


Recall that the refrigeration cycle goes through pressure and temperature changes. So the refrigerant oil needs to be able to lubricate throughout all the system’s pressures and temperatures.


Refrigerant oils need to be durable in real world use. They cannot break down easily or decompose, throughout all pressure and temperature changes.


In order for refrigerant oils to do their job, it is important to consider the following properties:

  1. Viscosity

  2. Miscibility

  3. Hygroscopy

  4. Hydrolysis

  5. Flammability

2. Viscosity


Oils have different levels of viscosity. Viscosity is how thick the oil is. The thicker an oil, the slower it flows.


Imagine pouring water on a pan compared to pouring olive oil on a pan. The oil moves out more slowly than the water. This means the oil is more viscous.


The more viscous an oil is, it harder it is to move refrigerant through the system. So the harder it is to transfer heat, which defeats the whole purpose of the refrigeration cycle.


3. Miscibility

Miscibility is how well the oil mixes and moves with the refrigerant.


Refrigerant oil needs to be miscible with refrigerant. This means it needs to mix well with refrigerant in order for the refrigerant to do its job of transferring heat.


If an oil is not miscible with the refrigerant in the system, it will cause inefficiencies in the refrigeration cycle. This can make equipment fail, since it adds a stress to it.


4. Hygroscopy


Many of the oils we used today are hygroscopic. This means they attract moisture and retain it.


This contaminates the system, so we need to keep these oils away from moisture.


Moisture in a refrigeration system can cause serious problems. Water in the system can freeze, which creates an obstruction in the piping. It’s like a blood clot of sorts. This leads to ineffective cooling in the system.


5. Hydrolysis


Hydrolysis is when water breaks something down. For our purposes, we are concerned with how refrigerant oils will react with water.


Some oils will react with water and decompose into acids and alcohol. If this happens, it will cause damage to equipment components. The resulting acid will damage any metal equipment.


Technicians must also consider that this oil will be cycled through the system for up to millions of times. The oil cannot decompose even with millions of times of being run through the cycle.

There are a lot of units that have been operating with the original refrigerant and oil for 30-40 years. Systems can function well with proper design and maintenance.

6. Flammability


In order to operate safely, these oils must not be flammable or explosive at the system’s temperatures and pressures. To determine what oils should be used, there are flammability tests that can be performed.

This is done by organizations like ASHRAE that provide guidelines on what oils should be used. The technician just needs to follow these guidelines and understand where it comes from.


7. Conclusion


In this module, we looked at the purpose and properties of refrigerant oils.


Question #1: An ideal oil is readily miscible with the refrigerant in the system.

  1. True

  2. False

Scroll down for the answer...









Oils need to be miscible, or mix well, with refrigerant in the system.


Question #2: As long as an oil is not flammable at the starting and ending temperature, it can be used because the system is contained.

  1. True

  2. False

Scroll down for the answer...















The oil needs to be non-flammable at all temperatures and pressure of the system.


Question #3: An ideal oil is best at handling high temperatures and high pressures.

  1. True

  2. False

Scroll down for the answer...
















Oils need to handle all pressures and temperatures in the system. This includes the maximum and minimum of all pressures and temperatures.



Question #4: Hydrolysis is when refrigerant oils break down in the presence of water.

  1. True

  2. False

Scroll down for the answer...


























False! The majority of ozone is located in the Stratosphere, not the Troposphere.


Question #5: Hygroscopic oils


  1. Break down in the presence of water

  2. Absorb moisture readily

  3. Reject moisture readily

  4. None of these

Scroll down for the answer...











Hygroscopic oils absorb water easily. This is different than hydrolysis, which would be (a).


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