Why should a technician not go above 10 psig when leak testing an R-123 chiller?
Trade training teaches a ceiling of 10 psig, to stay safely below the rupture disc. Neither 40 CFR Part 82 nor EPA's test outline sets that number, and the chiller manufacturer's limit takes priority.
- To stay safely below the rupture disc settingCorrect answer
- Nitrogen dissolves into R-123 above 10 psig
- Table 1 caps test pressures at 10 psig
- The purge unit shuts down above 10 psig
Why “To stay safely below the rupture disc setting” is correct
Low-pressure chiller shells are built for low pressures and protected by a rupture disc, which on Trane CenTraVac chillers breaks at 15 psig. Pushing a test past 10 psig risks blowing the disc and releasing the whole charge, so 10 psig is the commonly taught ceiling. A manufacturer may set a lower one, such as Trane's 8 psig.
Source: EPA: Test Topics; Trane CVHE-SVX005E-EN, CenTraVac IOM (15 psig rupture disk); Trane CTV-SVX05H-EN, R-123 handling guide (8 psig leak test)
Why the other answers are wrong
- Nitrogen dissolves into R-123 above 10 psig — Dissolving nitrogen is not why the limit exists.
- Table 1 caps test pressures at 10 psig — Table 1 sets evacuation levels, not leak test pressures.
- The purge unit shuts down above 10 psig — The purge unit is not the reason for the test pressure limit.
The source, word for word
Order of preference of leak test pressurization methods for low-pressure systems
Hot water method or built-in system heating/pressurization device such Prevac
This one rests partly on trade knowledge. EPA's outline covers how to pressurize a low-pressure system for a leak test but gives no pressure limit, and neither does 40 CFR Part 82. The 10 psig figure comes from trade training. Manufacturers publish their own numbers, and Trane's literature lists a 15 psig rupture disk on CenTraVac chillers and an 8 psig nitrogen leak test.
How to pressurize it
EPA's outline gives an order of preference. Try hot water in the tubes or a built-in device such as Prevac first, and use nitrogen after that. Check the chiller's own literature before adding any test pressure, because blowing the rupture disc can release the charge.
The nitrogen rule people mix up with this
Section 82.156(a)(1)(ii) limits using nitrogen on some low-pressure appliances, but it covers pressurizing to 0 psig before opening one for a non-major repair. It is not a leak test rule. Why nitrogen is the usual test gas covers the wider question.
Keep practicing
- Which gas to use for leak testing
- Why vapor goes in before liquid on an R-123 chiller
- The evacuation level for disposing of a low-pressure chiller
- EPA 608 Type 3 practice test
- EPA 608 Type 3 mock exam
Unofficial, not affiliated with the EPA or any EPA-approved certifying organization. Questions are original practice written from public EPA material, not real exam questions.