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What Happens If You Put R134a in an R12 System?

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There are many answers to the question of whether or not you can put R134a refrigerant into an R12 system, and that’s for good reason. R134a and R12 are two different types of refrigerant used in A/C and refrigeration systems, and while they have the same function (cooling), they are actually opposites of one another. That’s why knowing what type of refrigerant system you’re working with is crucial to its functionality, longevity and safety. 

We’ll explore the reasoning and answers about what can happen if R134a is used in an R12 system, and the adverse effects it can cause. Please note that it’s ill-advised—and also illegal—to use R143a in an R12 system that hasn’t been converted or totally retrofitted, and purged of any and all R12.

What are the Differences Between R134a and R12 Refrigerant? 

While both R12 and R134a are refrigerants and are used for cooling and refrigeration, they are two different compounds entirely. R12 (also known as “Freon”) is a CFC (chlorofluorocarbon), specifically dichlorodifluoromethane, and R134a is a hydrofluorocarbon (HFC), meaning both have different chemical makeups. Additionally, CFCs are known to be damaging to the ozone, which is why R12 is no longer in production. R134a is a safer replacement for R12. 

Another major difference is the type of oil both refrigerators require. R12 is compatible with mineral oil, and most R12 systems use this. R134a uses Polyalkylene Glycol (PAG) oil. One commonality both R134a and R12 share is that they are compatible with Polyol Ester Oil (POE). 

Finally, R134a is much smaller than R12 on the molecular level, and thus moves and behaves differently. 

What Can Happen if you Use R134a in an R12 System?

To be able to use R134a in an R12 system, the R12 system needs to undergo a retrofitting so that it’s able to handle and process R134a refrigerant. This also means that some refrigerant conversion needs to be done in order to drop R134a into a R12 system. On top of the retrofitting, the R12 system needs to be properly cleared of the refrigerant. Once that’s complete, then you can use R134a in an R12 system.

However, what happens if R134a was used on an R12 system that wasn’t converted, or retrofitted and cleared?

With the differences between the two refrigerants in mind, it goes without saying that charging an R12 system with R134a can have some serious negative effects.

Refrigerant Can Leak Easier

For starters, R12 systems and R134a systems are designed differently to accommodate the gaseous state of each. R134a systems work at higher discharge-side pressures than R12 systems, which could lead to compressor seals leaks. Additionally, since R134a is composed of much smaller molecules, it has a greater chance of leaking from an R12 system. 

Oil Can Be Incompatible

Another issue comes into play with the type of oil used in the system. As previously stated, R12 systems usually use mineral oil, which is incompatible with R134a. When R134a comes into contact with mineral oil, it can hinder the oil from returning to the compressor, or possibly reduce heat transfer. This means that the mineral oil cannot be dispersed through the system properly, which can then lead to significant damage to the internal compressor and refrigeration system that will be costly to repair. This is why PAG and POE exist as alternatives to use with R134a.

Can You Legally Use R134a in an R12 System?

Ultimately, no. If you’re trying to “top off” an R12 system with R134a refrigerant, you can face some hefty fines with the Federal US government and EPA. In order to legally use R134a refrigerant in an R12 system, it must be converted or retrofitted to be able to properly use R134a, and all R12 must be properly discharged and captured prior to charging with R134a.