A running low-pressure chiller develops an opening in a section of shell that is below atmospheric pressure. What passes through that opening?
Correct Answer
B) Air and moisture are pulled into the machine
Fluids move from higher pressure toward lower pressure. The evaporator side of a running low-pressure chiller sits below atmospheric pressure, so the room is the high side and the machine is the low side. Air, along with the water vapor it carries, is pushed into the shell. That is the opposite of what happens on a high-pressure machine, where a leak sends refrigerant out into the room. It is also why a low-pressure machine can have a real leak and still show nothing on a hand held detector.
Why This Is the Correct Answer
With the shell under a vacuum, atmospheric pressure outside is greater than the pressure inside, so the flow is inward. The machine takes in air and moisture, which show up later as non-condensables in the condenser and as acid and moisture in the oil. Refrigerant cannot flow out against that pressure difference while the machine is running.
Why the Other Options Are Wrong
Option A: Liquid refrigerant sprays out under its own pressure
Liquid needs pressure behind it to spray. The evaporator is under a vacuum, so there is no driving pressure pushing liquid out through the opening.
Option C: Refrigerant vapor escapes steadily into the machine room
Vapor escaping to the room is what happens on a high-pressure machine. Here the pressure gradient runs the other way, so vapor stays in while air comes in.
Option D: Nothing moves in either direction until the machine is shut down
A pressure difference exists any time the machine is running in a vacuum, so flow starts immediately. The opening does not wait for a shutdown to do damage.
Memory Technique
Vacuum sucks. A machine in a vacuum drinks air; a machine under pressure spits refrigerant.
Reference Hint
Low-pressure appliances operate below atmospheric pressure, so leaks on the vacuum side draw air in rather than push refrigerant out.
More epa-608-type-3 Questions
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?
What happens if the internal pressure of a low-pressure chiller is driven past the rating of its rupture disc?
Which refrigerant was the original factory charge in most low-pressure centrifugal chillers built during the nineteen sixties and seventies?
A technician is assigned to recover the charge from a large water chiller holding nine hundred pounds of R-134a. Which certification does that job require?
Into which appliance category does a machine charged with R-13 for very low temperature service fall?
On a low-pressure centrifugal chiller running at load, how do the evaporator and condenser sit relative to atmospheric pressure?
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