What property of the refrigerant is what actually places an appliance into the low-pressure category?
Correct Answer
C) A boiling point above 50 degrees F at normal atmospheric pressure
Low-pressure refrigerants boil at a temperature above 50 degrees F when they are open to the atmosphere, which is another way of saying their saturation pressure is very low at ordinary room temperatures. Because of that, the evaporator of a machine using one of these refrigerants sits in a vacuum whenever it is running. Charge size does not define the class, and neither does the way the compressor is built. A refrigerant with a saturation pressure above 355 psia at 104 degrees F is at the opposite end of the scale and describes a very high-pressure appliance.
Why This Is the Correct Answer
The class is defined by the refrigerant's pressure and temperature behavior. Low-pressure refrigerants such as R-11 and R-123 boil above 50 degrees F at atmospheric pressure, so at normal indoor temperatures their saturation pressure is below atmospheric. That single property is what forces the vacuum operation, the purge unit, and all the special Type III service rules.
Why the Other Options Are Wrong
Option A: A total system charge of five pounds or less at any time
Charge size is what separates small appliances from everything else. A five-pound limit describes Type I equipment, while low-pressure centrifugals hold hundreds of pounds of refrigerant.
Option B: A saturation pressure above 355 psia at 104 degrees F at rest
A saturation pressure that high at 104 degrees F describes a very high-pressure refrigerant such as R-13, which sits at the opposite end of the scale from a low-pressure machine.
Option D: A hermetically sealed compressor housing assembled at the factory line
Factory hermetic sealing describes how small appliances are built and charged on an assembly line. Low-pressure chillers are field-charged and field-serviced, so construction method does not classify them.
Memory Technique
Low pressure boils high: the boiling point is above room-cool 50 degrees F, so the machine has to suck itself into a vacuum to get cold.
Reference Hint
Appliance definitions live in 40 CFR 82.152; low pressure means the refrigerant boils above 50 degrees F at atmospheric pressure.
More epa-608-type-3 Questions
Which piece of equipment requires a technician to hold Type III certification before it may be serviced?
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 running low-pressure chiller develops an opening in a section of shell that is below atmospheric pressure. What passes through that opening?
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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