After a low-pressure machine is closed back up following an open repair, what has to happen before the charge goes in?
Correct Answer
B) Evacuate the machine to pull out the air and moisture it took on while open
A machine that has been open to the room is full of air and water vapor. Both have to come out before the refrigerant goes in, and evacuation is what removes them. Relying on the purge unit instead is a common shortcut and a poor one: the purge is sized to handle the small amount of air that leaks in during normal operation, not a shell full of it, and every purge cycle carries refrigerant out with the air. Evacuating first protects the charge, the oil and the machine's efficiency.
Why This Is the Correct Answer
Evacuation lowers the pressure enough to boil off moisture and to pull the air out of the vessel before any refrigerant is added. That leaves the machine clean and dry so the charge is not immediately contaminated with non-condensables and the purge unit is not asked to do work it was never sized for.
Why the Other Options Are Wrong
Option A: Charge the machine and let the purge unit remove whatever air is left
The purge unit handles the small ongoing air load of normal operation. Making it clear a shell full of air wastes refrigerant and takes a very long time.
Option C: Fill the machine with nitrogen and leave it under pressure until startup
Nitrogen under pressure is fine for storage or leak testing, but it must be removed by evacuation before charging, so this skips the necessary step.
Option D: Run the chilled water pumps for an hour so the tubes dry out
Running water pumps warms the tubes but does nothing about the air and moisture inside the refrigerant side of the machine.
Memory Technique
Evacuate for the load, purge for the leak. Purge units sip, they do not gulp.
Reference Hint
A machine opened for repair must be evacuated to remove air and moisture before charging; the purge unit is only for normal operating air ingress.
More epa-608-type-3 Questions
Some jobs on a chiller count as a major repair under the refrigerant rules, which changes what a technician is allowed to do with a badly leaking machine. Which job falls into that category?
An owner asks how many pounds of refrigerant the rules allow to be left inside a chiller once the recovery has been signed off. What is the correct answer to give him?
The motor of a hermetic centrifugal chiller sits inside the pressure boundary rather than outside it on a shaft. What follows from that construction?
An oxygen monitor is used to decide whether a chiller machine room is safe to enter after a refrigerant release. Below what oxygen reading is the atmosphere treated as oxygen deficient?
A low-pressure chiller's rupture disc has a discharge line running from it. Where does that line have to terminate?
A refrigerant vapor detector in a chiller machine room reaches its alarm level. Besides sounding, what is that alarm expected to do?
Which piece of equipment requires a technician to hold Type III certification before it may be serviced?
What property of the refrigerant is what actually places an appliance into the low-pressure category?
During normal operation, what condition exists inside the evaporator of a running low-pressure centrifugal chiller?
In what unit is the required final recovery vacuum for a low-pressure appliance normally expressed?
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