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