A chiller holds a standing vacuum test overnight without losing anything, yet its purge runs constantly once the machine is back in operation. Where should the technician look?
Correct Answer
C) At the compressor shaft seal, because it seals a turning shaft and only leaks once the machine is running
A standing test checks a machine at rest, and most joints behave the same way whether the machine is running or not. The shaft seal on an open drive machine is the exception: it seals against a rotating shaft, and it can be tight at standstill while leaking as soon as the shaft turns and the seal faces separate slightly. A machine that holds a static test but drinks air in operation points straight at it.
Why This Is the Correct Answer
The distinguishing feature is that the leak depends on motion rather than on pressure. A shaft seal has to seal a shaft that is turning at high speed, and film thickness, alignment and wear all change once it does. That makes it the one leak path that a static test cannot reproduce, which is why the two results appear to contradict each other.
Why the Other Options Are Wrong
Option A: At the tube bundle, because water only crosses into the shell when the chilled water pumps are running
A tube leak lets water in whether the pumps run or not, and it would show as a rise during the standing test as well.
Option B: At the condenser flanges, because they are the joints that see the highest pressure while the machine runs
Condenser flanges do see the highest pressure during operation, but a static test at the same or higher pressure would have found a leak there.
Option D: At the purge unit's own float, because it can only be tested with the machine at operating pressure
A purge float problem would show as a purge that runs without discharging, not as air genuinely entering the machine.
Memory Technique
Still machine, still seal. Spin it and the seal tells the truth.
Reference Hint
A standing vacuum test cannot reproduce a leak at a rotating shaft seal, which only opens once the machine is running.
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?
People Also Study
Business & Financial Management
120 questions · 70% to pass
Contract Administration
60 questions · 70% to pass
Project Management
60 questions · 70% to pass
Related Study Resources
Previous Question
A chiller's purge unit that once ran a few minutes each hour is now running nearly continuously. What does that tell the technician?
Next Question
A centrifugal compressor works differently from the reciprocating and scroll compressors used on high-pressure equipment. How does it raise the pressure of the vapor?