The motor of a hermetic centrifugal chiller sits inside the pressure boundary rather than outside it on a shaft. What follows from that construction?
Correct Answer
B) The motor is cooled by refrigerant, so a winding burnout contaminates the whole charge
On a hermetic machine, liquid or vapor refrigerant is routed over the motor windings to carry heat away, which is why the motor sits inside the pressure boundary. It makes for a compact, quiet machine with no shaft seal to leak, but it also means that a burned out motor puts acid and combustion products directly into the refrigerant and the oil. The charge from a burnout goes to a reclaimer, and the machine gets a thorough cleanup.
Why This Is the Correct Answer
Refrigerant cooling of the motor is what allows the motor to live inside the sealed circuit. The trade is that the refrigerant and oil share a space with the windings, so an electrical failure contaminates the charge with acid and carbon. That is why burnout cleanup on a hermetic chiller is a major job and why the recovered charge cannot go back in.
Why the Other Options Are Wrong
Option A: The motor is cooled by machine room air drawn through a filtered louver on the housing
A hermetic motor is inside the refrigerant circuit and has no path to room air at all.
Option C: The motor is cooled by chilled water routed through a jacket around the stator housing
Chilled water stays inside the tubes. Routing it around the motor would put a water leak directly into the windings.
Option D: The motor is cooled by the oil charge, so an oil analysis reports the winding temperature
Oil carries some heat away, but the motor is refrigerant cooled, and oil analysis reports moisture and acid rather than temperature.
Memory Technique
The motor breathes refrigerant. When it burns, the refrigerant breathes smoke.
Reference Hint
Hermetic compressor motors are cooled by refrigerant, so a burnout contaminates the charge and the oil with acid.
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?
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?
What should a technician do about the water in the chiller tubes before pulling a deep vacuum on the machine?
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