A technician is charging vapor into an evacuated R-11 chiller. At what point is it safe to switch to charging liquid?
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
A technician is charging vapor into an evacuated R-11 chiller. At what point is it safe to switch to charging liquid?
- When the pressure is above the saturation pressure for 32 °FCorrect answer
- When the shell pressure reaches 0 psig
- After exactly 10 pounds of vapor have gone in
- As soon as the purge unit starts running
Why “When the pressure is above the saturation pressure for 32 °F” is correct
Liquid will not boil below freezing once the chiller pressure is above the saturation pressure that matches 32 °F. Until then, vapor is charged; after that, liquid can be added without freezing the water in the tubes.
Source: EPA: Test Topics
Why the other answers are wrong
- When the shell pressure reaches 0 psig — Liquid can be safely added well before atmospheric pressure, once the 32 °F point is passed.
- After exactly 10 pounds of vapor have gone in — The switch point depends on pressure, not a fixed weight.
- As soon as the purge unit starts running — Purge operation does not tell you when liquid charging is safe.
Practice more of this
More EPA 608 Type III practice questions, or see every EPA 608 practice test.
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