Assessment and Evaluation Flashcards

What is the maximum pressure allowed when pressurizing a low-pressure (R-123) chiller for a leak test?

Answer: 10 psig

Low-pressure chillers should not be pressurized above 10 psig, so the 15 psig rupture disc does not burst.

What is the preferred way to raise pressure in a low-pressure chiller for a leak check?

Answer: Use controlled hot water or the system's heating blankets

Warming the refrigerant with controlled hot water or heating blankets raises pressure safely without bringing contaminants into the system.

What does excessive purge unit run time on a low-pressure chiller usually indicate?

Answer: Air is leaking into the chiller

Low-pressure chillers operate below atmospheric pressure, so frequent purging means air and moisture are leaking in.

Bubbles appear in the liquid-line sight glass of an operating system. What could this indicate?

Answer: A low refrigerant charge or a restriction upstream

Flash gas in the liquid line is usually caused by an undercharge or a pressure drop from a restriction.

Water from the chiller tubes is not circulated or drained while refrigerant is being recovered from a water-cooled chiller. What can happen?

Answer: The water in the tubes can freeze and rupture them

Refrigerant pressure and temperature drop during recovery, so still water in the tubes can freeze and crack them.

When charging an evacuated low-pressure chiller, why is refrigerant vapor added first instead of liquid?

Answer: To avoid freezing the water in the tubes until the pressure rises above saturation at 32°F

Liquid flashing at deep vacuum gets cold enough to freeze tube water, so vapor is added until the saturation temperature is above 32°F.

Which leak-detection method works by detecting the high-frequency sound of gas escaping through a small opening?

Answer: Ultrasonic leak detector

Ultrasonic detectors pick up the high-frequency hiss of a leak and work with any pressurized gas.