EPA 608 Core Chapter 7
Refrigerant Oils Overview
In this module, we will introduce how oils are used in HVAC. Skip to quiz!
Purpose of Oils
In HVAC systems, we use refrigerant oils in the compressor. As the 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.
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 inefficiently. An oil sample confirms whether this is happening.
After any major component failure or major leak, you need to take an oil sample. This includes the case of compressor burnout, which we will talk more about in the next chapter.
In this module, we looked at the purpose and properties of refrigerant oils. We also discussed the different types of oils and their applications.
Refrigerant Oils Properties
In this module, we will discuss the purpose of refrigerant oils and also go through their properties. Skip to quiz!
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:
Viscosity
Miscibility
Hygroscopy
Hydrolysis
Flammability
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 oil is, it harder it is to move the refrigerant through the system. So the harder it is to transfer heat, which defeats the whole purpose of the refrigeration cycle.
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 stress to it.
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.
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 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.
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.
In this module, we looked at the purpose and properties of refrigerant oils.
Types of Refrigerant Oils
In this module, we will discuss the different types of refrigerant oils and their applications in HVAC systems. Skip to quiz!
Mineral Oils
There are two main types of refrigerant oils:
Mineral Oils, and
Synthetic Oils
Mineral oils (MO) were first derived from petroleum refining processes. They are produced as a by-product when crude oil is distilled to produce gasoline.
Mineral oil was primarily used with the older generation of refrigerants, including CFCs and HCFCs.
Synthetic Oils
Mineral oils were great for the earlier generations of refrigeration systems with CFCs and HCFCs. As the industry phased out CFCs and HCFCs, it had to develop new oils to use with newer refrigerants.
These new oils are called synthetic oils. Synthetic oils are produced from processed petroleum in order to contain specific properties to work with new refrigerants.
Synthetic oils are required while making retrofits because mineral oils are not miscible with modern refrigerants. This means that mineral oils do not mix well with new refrigerants, which prevents refrigerants from doing their job.
Synthetic oils include:
Alkylbenzene (AB)
Polyolester (POE)
Polyalkylene Glycol - (PAG)
Polyvinyl Ether (PVE)
Each of these synthetic oils are used with different refrigerants.
Recall that an oil needs to be miscible with a refrigerant in order for the oil to work in a system containing that refrigerant. For example, let’s say an oil is used in a system with HCFC refrigerant. That means the oil has to be miscible with HCFC refrigerant.
Alkylbenzene (AB) is a synthetic oil used in refrigerant systems with CFC or HCFC refrigerants. As we discussed previously, CFCs and HCFCs have been phased out. But HCFCs are still used in blends.
So, for blends containing HCFCs, we need to use alkylbenzene (AB) to service the system.
Polyolester (POE) is a synthetic oil used in refrigeration systems that contain HFC and HFO refrigerants. These oils are also called ester oils.
This means that if a system is retrofitted with HFC refrigerant or HFC refrigerant blends, we need to use polyolester oil. Recall that retrofitting means modifying a system to use a new refrigerant.
Polyester oils, or ester-based oils, cannot be mixed with any other oils. This is something technicians have to keep in mind when servicing equipment using ester-based oils.
Polyalkylene Glycol (PAG) is a synthetic oil that is used mainly in-car air conditioning systems.
And lastly, polyvinyl ether (PVE) is a synthetic oil that is an alternative to POE oils.
In this module, we discussed the different types of oils and their applications.
Question #1: An ideal oil is readily miscible with the refrigerant in the system.
True
False
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Answer: True
Oils need to be miscible, or mix well, with refrigerant in the system.
Question #2: As long as oil is not flammable at the starting and ending temperature, it can be used because the system is contained.
True
False
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Answer: False
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.
True
False
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Answer: False
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.
True
False
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Answer: True
This is what hydrolysis is. Oils can break down into acids in the presence of water. This can damage the system equipment.
Question #5: Hygroscopic oils
Break down in the presence of water
Absorb moisture readily
Reject moisture readily
None of these
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Answer: Absorb moisture readily
Hygroscopic oils absorb water easily. This is different than hydrolysis, which would be (a).
Question #6: Alkylbenzene (AB) oil is used for systems with which of the following refrigerants? (Select all that apply)
CFC
HCFC
HCFC blends
HFC
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Answer: HCFC
HCFC blends
Alkylbenzene is used with systems that contain HCFCs. This includes systems that contain blends with HCFCs.
Question # 7: Alkylbenzene (AB) oil is miscible in HCFC refrigerant.
True
False
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Answer: True
Alkylbenzene is used with systems that contain HCFCs. This means it has to be miscible with HCFC refrigerants.
Question # 8: If we are retrofitting a system to use R-134a, which oil do we need to use?
Alkylbenzene (AB)
Polyolester (POE)
Mineral Oil (MO)
None of these. Retrofitting does not require oil use.
Scroll down for the answer...
Answer: Polyolester (POE)
We need to use polyolester oil (POE) with all HFC refrigerant applications. Since R-134a is an HFC refrigerant, we need to use POE.
Question #9: Polyolester oils are great because they can mix with a lot of other oils.
True
False
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Answer: False
This is false. Polyolester oils cannot be mixed with any other oils.
Question #10: R-1234yf is not miscible in any refrigerant oils.
True
False
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Answer: False
This is false. R-1234yf is an HFO refrigerant. HFO refrigerants can be used with POE oils, meaning that HFOs are miscible with POE oils. So R-1234yf is miscible in POE oils