Low pressure appliance
Short answer · Updated 2026
A low-pressure appliance uses a refrigerant with a liquid-phase saturation pressure below 45 psia at 104 degrees F, such as R-11, R-123, R-113 or R-245fa (40 CFR 82.152). These are mostly large centrifugal chillers that run partly in a vacuum, so leaks pull air in rather than push refrigerant out. Servicing or disposing of them requires Type III or Universal certification.
EPA 608 appliance pressure classes
| Class | Saturation pressure at 104 F | Example refrigerants | Certification |
|---|---|---|---|
| Low pressure | Below 45 psia | R-11, R-123, R-113, R-245fa | Type III |
| Medium pressure | 45 to 170 psia | R-12, R-134a, R-114, R-124, R-500 | Type II |
| High pressure | 170 to 355 psia | R-22, R-410A, R-407A, R-407C, R-502 | Type II |
| Very high pressure | Above 355 psia, or critical temperature below 104 F | R-13, R-23, R-503, R-508A, R-508B | Type II |
| Small appliance | Any, if factory sealed with 5 lb or less | Household refrigerators, window units | Type I |
A low pressure appliance is defined by its refrigerant: one with a liquid-phase saturation pressure below 45 psia at 104 degrees F, with R-11, R-123, R-113 and R-245fa as the regulation's examples. The other classes are drawn on the same scale: medium pressure runs from 45 to 170 psia (R-12, R-134a, R-124, R-114, R-500), high pressure from 170 to 355 psia (R-22, R-410A, R-407A, R-407C, R-502), and very high pressure above 355 psia or with a critical temperature below 104 degrees F (R-13, R-23, R-503, R-508A, R-508B). In practice the low pressure class describes large chillers used for building scale cooling, built around refrigerants that boil at unusually high temperatures relative to other working fluids, so much of the circuit spends its working life in vacuum territory, and that inversion changes the character of the equipment.
The defining consequence is the direction of leakage. A system running above atmospheric pressure pushes refrigerant out through any leak. A system running below atmospheric pressure draws air and moisture inward instead, which is why low pressure machines are associated with purge devices that separate and expel the air that inevitably finds its way in. Service thinking runs in reverse on these machines, and equipment and practices are specialized accordingly.
Within Section 608, low pressure appliances form their own certification category: Type III. The exam's Type III section is built around this class, testing the pressure concepts, the evacuation expectations, and the handling implications that follow from operating below atmosphere. A candidate pursuing Universal certification meets low pressure equipment as one of the three worlds the credential spans, alongside small appliances and the medium and high pressure class.
Common questions
What refrigerants are used in low-pressure appliances?
The regulation names R-11, R-123, R-113 and R-245fa as examples. All have a liquid-phase saturation pressure below 45 psia at 104 degrees F. R-123 is the one most technicians meet today, in centrifugal chillers.
How must a low-pressure appliance be prepared before it is opened?
It must be pressurized to no higher than 0 psig before opening (40 CFR 82.156). If the refrigerant boils above 85 degrees F at atmospheric pressure, you must use heat to raise the internal pressure as far as possible, and may then use nitrogen only to bring it the rest of the way to atmospheric pressure.
Why do low-pressure chillers have purge units?
Because much of the system operates below atmospheric pressure, any leak draws air and moisture in. A purge unit separates that non-condensable air from the refrigerant and vents it, which is why purge run time is a practical leak indicator on these machines.
Sources
- 40 CFR 82.152, definitions of low-, medium-, high- and very high-pressure appliances.
- 40 CFR 82.156, requirements for opening low-pressure appliances.
- 40 CFR 82.161, technician certification types.
Related terms
| Vacuum | Pressure below atmospheric, measured in inches or millimeters of mercury, used as the yardstick for refrigerant removal. |
| Evacuation | Pulling an appliance down to a specified vacuum to demonstrate that its recoverable refrigerant has been removed. |
| Refrigerant | The working fluid that absorbs and releases heat as it cycles between liquid and vapor inside a refrigeration system. |
The 608 fact sheet, free
Every verified 608 number on one printable page: the four types, the exam structure, the leak-rate and recovery figures. Enter your email and we will send you straight to it.
No spam. One useful sheet and occasional notes.