How should a zeotropic blend such as R-407C be charged into a system to keep its composition correct?
Substitute refrigerants and oils · EPA 608 Core. The correct answer, and the reasoning behind it.
Why there are no true drop-in replacements, and fractionation in blends.
The question
How should a zeotropic blend such as R-407C be charged into a system to keep its composition correct?
- As liquid from the cylinderCorrect answer
- As vapor from the top of the cylinder
- As vapor, with the cylinder warmed first
- Alternating vapor and liquid in small amounts
Why “As liquid from the cylinder” is correct
Because the components of a zeotropic blend boil at different temperatures, drawing vapor off the top of the cylinder pulls more of the lighter components and shifts the mix. Removing it from the cylinder as liquid keeps the blend at its designed composition.
Source: EPA: Test Topics
Why the other answers are wrong
- As vapor from the top of the cylinder — Vapor charging a zeotrope changes the composition through fractionation.
- As vapor, with the cylinder warmed first — Warming the cylinder does not stop vapor from fractionating.
- Alternating vapor and liquid in small amounts — Any vapor drawn from the cylinder can shift the mix.
Practice more of this
More EPA 608 Core practice questions, or see every EPA 608 practice test.
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