A rebuilt low-pressure chiller is ready to take its charge back after a complete retube. How does the technician establish how much refrigerant to put into it?
Correct Answer
B) Weigh in the charge the manufacturer's nameplate calls for, then check the evaporator level
The nameplate charge is the manufacturer's figure for that machine and that tube bundle, and the charge is weighed in against it from cylinders on a scale. The evaporator sight glass level at design load is the confirmation, not the starting point. What came out is not a reliable target, because a machine being retubed has usually been leaking or has lost refrigerant through its purge, so the recovered quantity is short by an unknown amount.
Why This Is the Correct Answer
Charging a chiller is done by weight against the nameplate figure, with cylinders on a scale so the amount added is documented. The evaporator refrigerant level checked at load confirms the machine is right. Both numbers are needed: weight gets the charge close and repeatable, and the level check catches an error in either direction.
Why the Other Options Are Wrong
Option A: Add refrigerant until the condenser pressure matches a saturation chart at outdoor temperature
Condenser pressure follows load, water temperature and non-condensables as much as it follows charge, so it is far too loose a target to charge a machine by.
Option C: Add back exactly what came out of the machine, since that is the charge it was running on
The quantity recovered is what was left in a machine that was probably losing refrigerant. Using it as the target locks the shortage in permanently.
Option D: Add refrigerant until the purge unit stops cycling, which shows the machine is full enough
Purge run time responds to air in the machine, not to how much refrigerant is in it. A properly charged machine with a leak will purge just as often.
Memory Technique
Scale first, sight glass second. Guessing from pressure is not charging, it is hoping.
Reference Hint
A chiller is charged by weight to the manufacturer's nameplate figure and confirmed by the evaporator refrigerant level.
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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