Every air compressor needs lubricating oil. You can’t just use any type of refrigerant oil, as you may well know. You need a specific air compressor oil type. We are going to look at how to match the refrigerant oil type (POE, PAG, MO, AKB) to an air compressor type and refrigerant type (what oil for R22, R410A, R32, R134A freons, and so on) and look at refrigerant oil compatibility chart.
Here’s why we need to be very careful when selecting the air compressor oil type:
Putting the wrong oil type into a compressor can (and most probably will) lead to damaging electrical windings (short circuits) and compressor burnout. Further on, we also explain how to remove the burnt carbon residue caused by burnout (if left unattended, it can clog TXV, reversing valve, or filter drier).
Example: If you use a polyolester oil (POE oil) with an R-22 refrigerant, it will eventually lead to the motor’s electrical winding causing the compressor to burn out. That’s because PEO oil is more hygroscopic (mixes with water) and will produce alcohols or acids. These acids can eat through the insulating resin separating electrical windings in the motor. The result will be motor causing a short, leading to compressor burnout.
Namely, the type of refrigerant oil we choose depends on 3 specific elements:
- Compressor type. Different compressor oil types are needed for rotary, reciprocating, and scroll compressors.
- Refrigerant type. We will differentiate between CFC and HCFC refrigerants (R11, R12, R115, and R22) that mostly require mineral oils, and HFC refrigerants (R32, R134a, R32, R410a, R407c, etc.) that mostly require polyolester oils.
- Application. These include air conditioning, refrigeration, and so on.
First, we will have an overview of which oils we use for compressors. After that, we will check what type of oils are used for what refrigerants (refrigerant oil chart). We will also cover examples of which oil to use (and, more importantly, not to use) for R22, R134A, and R410A refrigerants:
Why We Use Refrigerant Oils And Types Of Refrigerant Oils
The internal parts of any compressor need to be lubricated. In many cases, we would just use regular oils to oil these components. However, with a closed refrigeration-cycle system like an air conditioner or a heat pump, we have to use refrigerant oil.
Refrigerant oil is simply the type of oil that is circulated with the refrigerator (like R-22, R-32, R-410a, R134a, and so on). Not any oil will do and not any oil will do for any refrigerant. Namely, the selected oil type has to be miscible with the refrigerant. Miscibility simply means that oil and refrigerant can be safely mixed in the line set and circulate to the air compressor.
Here are the most commonly used types of refrigerant oils we can choose from:
- Mineral oil (MO). Mostly used in resident air conditioning systems.
- Polyolester oil (POE).
- Alkylbenyene oil (AKB).
- Polyalkylene glycol oil (PAG).
- Polyalpha olefin (PAO).
When picking the right oil for your air compressor or HVAC system, you must choose the right type of refrigerant oil. Here is a refrigerant oil chart with an explanation of what type of oil is suitable for specific refrigerant:
Refrigerant Oil Chart
This chart includes general recommendations for the type of oils used for different refrigerants (specified by ASHRAE-designated numbers or R numbers). Do note that refrigerant oil type (as well as the weight of oil you need to use) can be found in the rating place.
Some compressors also have a rating plate that specifies the kind of refrigerant oil you need to use. That plate is your primary source for the oil type; the refrigerant oil chart is the secondary source (general recommendation only).
|Refrigerant:||Mineral Oil (MO)||Polyolester Oil (POE)||Alkylbenyene Oil (AKB)||Polyalkylene Glycol Oil (PAG)||Polyalpha Olefin (PAO)|
Sources include: ACHRNews, DuPont spreadsheet, and RefrigerationClub.
It is still essential that you use the air compressor oil that is specified by the manufacturer of the HVAC unit or the compressor itself.
Based on the refrigerant oil compatibility chart, you can tell which refrigerant oil you need. Here are just a few examples:
Example 1: What Oil Does A R22 Use? (Example 1)
R22 is a HCFC refrigerant (HydroChloroFluoroCarbon). As for most HCFC refrigerants, you should use mineral oil with R22. Alkylbenyene oil is a good alternative as well because it is miscible with R22 refrigerant.
Now, some retrofits of R22 such as R422A, R422D, and R417A are also miscible in mineral oil (with POE oil and ABK oils as good alternatives as well.
Others like more common R410A and R407C, however, are not miscible in mineral oil and you must not use mineral oil with either R410A or R407C. For R410A, you have to use POE oil. For R407C, you also have to use POE oil. This is because these two R22 retrofits are mixtures of R32, a refrigerant that is miscible with POE oil, not mineral oil.
What Type Of Refrigerant Oil Is Used In R134A Systems? (Example 2)
You will find the R134A refrigerant (tetrafluoroethane or R134A is an HCF refrigerant) in a lot of car air conditioning systems. The best type of oil for R134A system is polyolester oil (POE). Alternatively, you can also use polyalpha olefin (PAO).
It is essential that you don’t use mineral oil, PAG oil, or ABK oil with R134A refrigerant. Mineral oil is less hygroscopic than POE oil, for example. In a chain of events, using mineral oil in the R134A system will produce acids which will dissolve the resin between motor electrical winding and cause a short (since windings will now be touching). This can lead to compressor burnout.
What Oil Does R410A Use? (Example 3)
R410A freon will always use POE oil. Obviously, always check the rating plate for exactly the right choice of air compressor oil; you will never see mineral oil or PAG for R410A.
Hopefully, you now understand how important choosing the right oil type for freon type is. The freon oil chart will help you make the right choice.