A running low-pressure chiller has a leak at a joint on its condenser. What is happening at that joint while the machine is loaded?
Correct Answer
C) Refrigerant is escaping, because the condenser runs slightly above atmospheric pressure at load
A running low-pressure chiller is not under vacuum everywhere. The evaporator sits below atmospheric pressure, but the condenser is pushed slightly above it as the machine rejects heat. A leak on the condenser therefore loses refrigerant while the machine runs, and it draws air in once the machine shuts down and the pressure falls back. That is why a detector can find a condenser leak on a running machine while the evaporator end shows nothing at all.
Why This Is the Correct Answer
The pressure profile across a running machine decides the direction of every leak on it. The condenser is above atmospheric at load, so a leak there pushes refrigerant out and can be found with an ordinary electronic detector. The same joint reverses direction on shutdown, which is why these machines both lose charge and accumulate air over a season.
Why the Other Options Are Wrong
Option A: Nothing moves either way, because the condenser sits exactly at atmospheric pressure at load
The condenser is above atmospheric at load rather than at it, which is exactly why a leak there behaves differently from one on the evaporator.
Option B: Air is drawn in, because every part of a low-pressure machine is under a vacuum at all times
The evaporator is under a vacuum; the condenser is not. Treating the whole machine as a vacuum vessel is the most common error on these questions.
Option D: Water vapor is drawn in, because the condenser is the coldest surface on the machine at load
The condenser is the hottest part of the machine at load, not the coldest, and nothing is drawing water vapor into it.
Memory Technique
Cold end sucks, hot end blows. The machine is a vacuum machine only at one end.
Reference Hint
On a running low-pressure chiller the evaporator is below atmospheric pressure and the condenser is slightly above it.
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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