A chiller has just been retubed and is being prepared to go back into service. What has to be done before the charge is returned to it?
Correct Answer
D) The water side is pressure tested and the shell is leak tested and then evacuated to dry it
A retube disturbs every tube-to-tube-sheet joint, so the water side is pressure tested to prove those joints hold before anyone puts refrigerant back into the shell. The refrigerant side is leak tested within the low pressure ceiling that applies to these machines, and then the shell is evacuated to pull out the air and moisture it took on during the weeks it stood open. Only after all three steps does the charge go back in.
Why This Is the Correct Answer
Three separate things have to be proven before a rebuilt machine is charged: that the new tube joints hold water, that the refrigerant side is tight, and that the shell is dry. Each has its own test, and skipping any one of them means either flooding the new bundle or charging a machine full of moist air, which starts acid formation on day one.
Why the Other Options Are Wrong
Option A: The purge unit is run for a day so the shell is cleared of the air it took on while open
A purge unit is not a substitute for evacuation. It removes gas slowly and cannot deal with the moisture the machine took on while it stood open.
Option B: The charge is weighed in slowly, and the machine is leak tested at operating pressure afterward
Leak testing after the charge is in leaves the technician with a machine full of refrigerant and a leak, which is the situation the tests exist to prevent.
Option C: The oil is changed after the first week of operation, once the new tubes have settled in
An oil change a week later does nothing about air and moisture that went in with the charge on the first day.
Memory Technique
Test the water, test the shell, dry the shell, then charge. Four steps, always in that order.
Reference Hint
A rebuilt appliance is leak tested and evacuated to remove air and moisture before the refrigerant charge is returned.
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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