Why is vapor charged before liquid into an evacuated R-123 chiller?
Liquid refrigerant boils very cold in a deep vacuum and can freeze the water in the tubes. Charging vapor first raises the pressure, so the liquid does not boil that cold when it goes in.
- Liquid would damage the compressor bearings
- Vapor charging is required to meet the evacuation levels in Table 1
- Liquid boils very cold in a deep vacuum and can freeze tube waterCorrect answer
- Vapor 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.
The source, word for word
Need to introduce vapor before liquid to prevent freezing of water in the tubes
Need to charge centrifugals through evaporator charging valve
EPA's outline states the vapor-first rule and the reason for it. The physics in the explanation is trade knowledge.
Charging an evacuated chiller
EPA's outline covers the order and the charging point. The tube water matters as well: keep it circulating, or drain it, while charging.
- Charge through the evaporator charging valve.
- Start with vapor, then move to liquid once the pressure is up.
- EPA's outline gives no pressure or vacuum figure for switching to liquid, so take that number from the chiller manufacturer's procedure.
Keep practicing
- The leak test pressure limit on an R-123 chiller
- The evacuation level for disposing of a low-pressure chiller
- Pressure-temperature chart basics
- EPA 608 Type 3 practice test
- EPA 608 Type 3 mock exam
Unofficial, not affiliated with the EPA or any EPA-approved certifying organization. Questions are original practice written from public EPA material, not real exam questions.