Why is vapor charged before liquid into an evacuated R-123 chiller?

Recharging techniques · EPA 608 Type III. The correct answer, and the reasoning behind it.

Charging vapor before liquid, and charging centrifugals through the evaporator valve.

The question

Why is vapor charged before liquid into an evacuated R-123 chiller?

• ALiquid would damage the compressor bearings
• BVapor charging is required to meet the evacuation levels in Table 1
• CLiquid boils very cold in a deep vacuum and can freeze tube waterCorrect answer
• DVapor carries the oil back into the sump

Why “Liquid boils very cold in a deep vacuum and can freeze tube water” is correct

At a deep vacuum, refrigerant boils at temperatures far below 32 °F. Liquid charged at that point flashes and chills the tubes enough to freeze the water and crack them. Vapor raises the pressure first so the liquid will not boil that cold.

Source: EPA: Test Topics

Why the other answers are wrong

• Liquid would damage the compressor bearings — The concern is freezing water in the tubes, not compressor bearings.
• Vapor charging is required to meet the evacuation levels in Table 1 — Table 1 sets evacuation levels, not charging methods.
• Vapor carries the oil back into the sump — Charging vapor first has nothing to do with oil return.

Practice more of this

More EPA 608 Type III practice questions, or see every EPA 608 practice test.