Type III — low-pressure appliancesDifficulty 3/5
When recharging a low-pressure centrifugal chiller, why is vapour introduced before liquid?
- ATo purge the non-condensable gases that collected while the system was open
- BTo confirm that the charging valve is clear before liquid refrigerant is added
- CTo allow the oil to warm to the temperature required before it can be removed
- DTo raise the temperature in the tubes so the water inside them does not freeze
Show answer and rationale
Correct: D. Liquid refrigerant entering an evacuated chiller flashes to vapour and chills the tubes sharply. Bringing the pressure and temperature up with vapour first removes that freezing risk, and charging goes through the evaporator charging valve.
- A — Non-condensables are removed by the purge unit, not by the order in which you charge.
- B — Valve clearance is confirmed before charging begins and is not the reason for the sequence.
- C — Heating oil to 130 degrees Fahrenheit concerns oil removal, which precedes recharging.