What distinguishes a 'high-pressure appliance' from a 'low-pressure appliance' under Section 608?
Not quite. The answer is A: The classification is by the refrigerant's liquid saturation pressure at 104 °F: high-pressure refrigerants (such as R-22 and R-410A) fall between 170 and 355 psia, while low-pressure refrigerants (such as R-123) fall below 45 psia, which means the low side of the system normally runs below atmospheric pressure
The pressure class is a property of the refrigerant, not the size or building type: high-pressure means a liquid saturation pressure of 170–355 psia at 104 °F (R-22, R-410A), low-pressure means below 45 psia (R-123, as in many centrifugal chillers). Refrigerants in between, such as R-134a (45–170 psia), are classed as medium-pressure — and the rule has Type II technicians cover medium-, high-, and very high-pressure appliances alike. Low-pressure systems run with their low side under vacuum, which is why their service and evacuation procedures differ so much.
Reference: 40 CFR Part 82 § 82.152; 82.161(a)(1) (Definitions of high-, medium-, and low-pressure appliance)
Checked against the official text
Read the eCFR text current through 2026-10-30 of § 82.152. Definitions are by liquid-phase saturation pressure at 104 °F: high 170–355 psia (e.g., R-22, R-410A), medium 45–170 psia (e.g., R-134a), low below 45 psia (e.g., R-123). § 82.161(a)(1)(ii) says Type II covers medium-, high-, and very high-pressure appliances.
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