Manual for Refrigeration Servicing Technicians - UNEP - Division of ...

4
Servicing Practices
Why charge refrigerant blends as liquids?
Refrigerant blends are simply a mixture of different refrigerant
components. If the blend is a zeotropic mixture (i.e. R4xx) and it is
charged as vapour, the refrigerant with the highest vapour pressure
will be charged at a higher proportion than the other component(s).
Charging as a liquid is the only way to guarantee that the blend is
charged within its intended composition.
Fractionation of a refrigerant blend (separation of the individual
components) can occur by removing the refrigerant from the
cylinder as a vapour instead of a liquid. This can potentially lead to
both safety and performance issues. As such, it is recommended
charging all blends in liquid phase only. From a safety standpoint,
a blend with an A1 safety classification – that has been composed
of non-flammable and flammable substances – will remain nonflammable,
even after fractionation has occurred.
Performance may be significantly affected, depending on the
extent of fractionation. If only a small amount of the refrigerant
placed into the system was charged as vapour, the blend may
perform adequately. The performance of systems containing
larger percentages of a blend charged as vapour is more likely to
be affected by fractionation. Typically, more of the high-pressure
components will be found in the system, and less in the cylinder.
Additionally, the refrigerant remaining in the cylinder may also be
compromised. In these cases, it is recommended contact technical
support of the refrigerant supplier.
It is also important to note that if the entire contents of a refrigerant
blend container (full cylinder) are charged into a system as vapour,
it will produce the same effect as charging the entire cylinder
as liquid. Also, certain refrigerant blends are more susceptible
to fractionation than others, and their stated temperature glide
provides an indication of this. For example, fractionation is a greater
concern when working with R409A (high temperature glide, ~ 8 K)
than when working with R410A (a small glide, < 1 K).
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