How does a technician tell when a recovery cylinder taking an R-123 charge has reached its filling limit?
- By keeping the cylinder on a scale and watching the net weight
- BBy waiting for the cylinder pressure to reach its marked service pressure
The service pressure marked on a cylinder is a design rating, not a fill indicator, and a low-pressure refrigerant will never approach it at room temperature.
- CBy feeling the outside of the cylinder for a frost line
Frost lines can suggest a liquid level on some cold refrigerants, but R-123 near room temperature produces no reliable frost line.
- DBy counting the running hours logged on the recovery machine
Run time varies with vapor density, hose size and machine condition, so it cannot be converted into pounds transferred. Two identical machines can take very different amounts of time to give up the same weight.
Why A is correct
Weight is the only dependable indicator with a low-pressure refrigerant, because its vapor pressure at room temperature is too low to move the cylinder gauge meaningfully. Working from tare weight and rated capacity lets the technician stop at the correct fill level rather than guessing.
What this question is testing
This tests measurement method rather than the fill limit number, and it checks that you understand why pressure based judgment fails with low-pressure refrigerants. It measures whether you can select a measurement method appropriate to the refrigerant rather than reaching for the pressure gauge habit built on high-pressure work.
On the job
Put the cylinder on the scale before you start and leave it there. On a long chiller recovery you may go through several cylinders, and the transitions are where mistakes happen: someone swaps cylinders, forgets to re-tare, and overfills. An overfilled cylinder of any refrigerant is a serious hazard if it warms up, because a liquid full cylinder has no vapor space to absorb thermal expansion. The scale is cheap insurance on a job that already takes all day.
Memory technique
No pressure, no clue. Weigh it, because the gauge will lie to you all day.
Exam tip
When a question involves a low-pressure refrigerant and a cylinder, expect the answer to involve weight. Pressure based methods do not work here.
Where to look it up
Recovery cylinder fill is judged by net weight on a scale, because low-pressure refrigerant develops almost no pressure at room temperature.