Tag: fractionation

I am consistently surprised by how much false information still circulates out in the field and one of the ones I hear often is the idea that you cannot or should not “top-off” or recharge R410a systems on top of an existing charge of R410a when the system is low.

So to be clear before we move on, it is 100% OK to add to an R410a charge without fear of any significant fractionation. If you doubt me, you can read THIS from Dupont/Chemours.

R410a is a near-azeotropic blend of 50% R32 and 50% R125. This means that while it has a tiny amount of temperature glide you can still work with it like a zero glide (azeotropic) refrigerant for all practical purposes.

The fear that some have is that if the refrigerant leaks out in vapor phase, one refrigerant will leak at a higher rate than another which could change the blend as it leaks.

While this can (and does) occur with high glide refrigerants, it has been proven that this is most likely to occur in very slow leaks during long periods of storage when the refrigerant is not moving. An example would be a high glide blend in a tank with a slow leak at the valve on top. This is the worst case scenario and an example of where fractionation can be a real issue.

In a running system or a system that runs most of the time, it is unlikely that fractionation would pose an issue because the movement of the refrigerant in the circuit mixes the refrigerant and prevents one part from leaking significantly faster than another. This study by Purdue covers this as it relates to flammability risks.

The practice of charging blends in liquid phase still makes good sense because fractionation, to the extent it occurs is still most likely to pose an issue in a static vessel like a tank and charging in the liquid state is just cheap insurance against fractionation.

But once again… It does no harm to top off an R410a system with R410a. This is NOT to say I’m advocating recharging systems without finding and repairing leaks where possible, just that fractionation isn’t a reason not to do so.

— Bryan


Over the years I have heard technicians say that refrigerant can wear out or “lose it’s blend” by sitting in a tank.

This does not happen… at least not like that

What can and does happen is called “Fractionation”. Refrigerant blends that are composed of a mix of refrigerants with different vapor and liquid PT characteristics known as Non-azeotropic, Zeotropic or in some cases near-azeotropic. All fancy words to mean that these refrigerant blends must be added or removed completely or in the liquid state to prevent more / less of one refrigerants in the mix to be added or removed than the other.  If the refrigerant is allowed to fractionate and some of it is added in the vapor only state both the refrigerant left in the tank, and the refrigerant added to the system will no longer have the designed properties of the listed refrigerant.

If one of the refrigerants in the blend leaks out faster, what you have left isn’t the same refrigerant

While all blends should all be charged in the liquid state, some refrigerants are more likely to be impacted by fractionation than others.

For example, R-410a  (50% R-32 & 50% R-125) has very little “glide” between liquid and vapor and so while it is a blend, it is less likely to fractionate severely when charged in the vapor phase (which you still shouldn’t do).

A refrigerant like R-407c ( a mixture of R32/125/134a) will fractionate much more easily resulting in far greater pressure/temperature swings and poor performance when it occurs.
Fractionation will often happen for three reasons

  1. A technician charged the system in vapor phase (tank upright) instead of in liquid phase (upside down)
  2. The tank had a small leak while stored upright
  3. The system has a significant leak.

The particular case of fractionation being caused by a system leak depends on many factors including what part of the system the leak occurs, the physical location of the leak and how much refrigerant leaked out. There was a study done at Purdue that shows that fractionation after leakage can be a factor in high glide systems like R407c.

The ramifications of this depend on the specific situation, but in some cases, the only viable option will be to completely recover and recharge with a virgin charge. This is not because refrigerant has “lost its mix” from sitting, but rather because some of the”mix” has left the tank or system at a different rate, leaving an improper mix behind.

— Bryan

 

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