The short answer
Before a non-small appliance is opened for major work, it must be evacuated to the level in EPA's Table 1 (40 CFR §82.156). The number depends on the appliance's pressure class, its charge size, and whether the recovery equipment was made before or after November 15, 1993. Low-pressure appliances are the odd row out: 25 mm Hg absolute, either era.
Table 1 — required levels of evacuation
| Appliance type | Equipment made before Nov 15, 1993 | Equipment made on/after Nov 15, 1993 |
|---|---|---|
| Very-high-pressure appliance | 0 in Hg | 0 in Hg |
| High-pressure appliance (or isolated component), full charge under 200 lb | 0 in Hg | 0 in Hg |
| High-pressure appliance (or isolated component), full charge 200 lb or more | 4 in Hg | 10 in Hg |
| Medium-pressure appliance (or isolated component), full charge under 200 lb | 4 in Hg | 10 in Hg |
| Medium-pressure appliance (or isolated component), full charge 200 lb or more | 4 in Hg | 15 in Hg |
| Low-pressure appliance | 25 mm Hg absolute | 25 mm Hg absolute |
All values are inches of Hg vacuum relative to standard atmospheric pressure (29.9 in Hg), except the low-pressure row, which is absolute. Pressure classes are defined in §82.152 by the refrigerant's saturation pressure at 104 °F: very-high (critical temperature below 104 °F, or above 355 psia), high (170–355 psia), medium (45–170 psia — R-134a lives here), low (below 45 psia — R-11, R-123, R-113, R-245fa).
The rules around the table
- Verify before you open. The technician must verify the required level has been reached — in the appliance, or in the isolated part being serviced — before opening it (§82.156(a)).
- Non-major work is different. If the work isn't major and the refrigerant won't be evacuated to the atmosphere afterward: medium/high/very-high appliances go to no higher than 0 psig; low-pressure appliances are pressurized to no higher than 0 psig, with openings covered when isolation isn't possible (§82.156(a)(1)).
- Oil changes on low-pressure appliances: evacuate or pressurize to no higher than 5 psig (§82.156(a)(1)(iii)).
- Leaks that block the target: isolate leaking from non-leaking components where possible; non-leaking parts still hit Table 1; the leaking part goes to the lowest attainable level, capped at 0 psig (§82.156(a)(2)).
- Small appliances aren't in this table. Type I recovery is percentage-based: 80% (pre-1993 equipment, or a dead compressor) / 90% (post-1993 equipment, compressor running), or evacuate to 4 in Hg vacuum (§82.156(b)).
Drill it
Table 1 is the most-tested table in Type II and Type III. Run the bins, then take the mixed exam.