EPA 608 Technician Certification: Low-Pressure Leak Detection and Leak Repair Concepts
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Overview
This chapter covers leaks in low-pressure chillers, which behave differently from leaks in other systems. You will learn why air gets in instead of refrigerant getting out, how to spot a leak, how to raise pressure safely for a leak test, and the leak repair rules for large chillers.
Low-pressure refrigerants such as R-11, R-123, and R-113 have a liquid saturation pressure below 45 psia at 104°F. Much of a running low-pressure chiller is below atmospheric pressure, so a leak lets air and moisture in. A purge unit that runs much more than usual is a key sign of a leak.
To leak test, raise the pressure first with controlled hot water or a built-in heating device, and use nitrogen only if needed. Do not go above 10 psig, because the rupture disc is usually set at 15 psig.
Chillers with 50 pounds or more of an ozone-depleting refrigerant such as R-123 must be repaired when the yearly leak rate is over 10 percent for comfort cooling or 30 percent for industrial process refrigeration. After exceeding the rate, comfort cooling chillers need a leak inspection once per calendar year. Leaking 125 percent or more of the charge in a year must be reported to EPA by March 1.
Key concepts
Low-pressure appliance
An appliance using a refrigerant with a liquid saturation pressure below 45 psia at 104°F, such as R-11, R-123, R-113, and R-245fa.
Memory tipR-11, R-123, R-113 = low.
Source: 40 CFR 82.152 (EPA Section 608 rules) · as of 2026
Leaks let air in
Parts of a running low-pressure chiller are below atmospheric pressure, so leaks pull air and moisture into the system instead of letting refrigerant out.
Memory tipExcessive purging = leak.
Leak test pressurizing
Preferred: controlled hot water or a built-in heating/pressurization device. Next: nitrogen. Do not exceed 10 psig.
Memory tipHeat first, nitrogen second, 10 psig max.
Source: EPA Section 608 Test Topics · as of 2025
Trigger leak rates
For appliances with 50 lb or more of ODS refrigerant: 10% comfort cooling, 30% industrial process refrigeration, 20% commercial refrigeration, per 12 months.
Memory tipComfort chiller: 10%.
Source: 40 CFR 82.157(c) (EPA Section 608 rules) · as of 2026
Automatic leak detection
A system that senses refrigerant in air can replace periodic inspections if it detects 10 ppm, alerts at 100 ppm, and is audited or calibrated every year.
Memory tipDetect 10 ppm, alarm at 100 ppm.
Source: 40 CFR 82.157(g)(4) (EPA Section 608 rules) · as of 2026
Chronic leak report
Owners of appliances with 50 lb or more that leak 125% or more of the full charge in a calendar year must report to EPA by March 1 of the next year.
Memory tip125% → March 1 report.
Source: 40 CFR 82.157(j) (EPA Section 608 rules) · as of 2026
Often tested
- Rupture disc is usually set at 15 psig, so leak test at 10 psig or less.
- Comfort cooling inspections after exceeding the rate: once per calendar year.
- Leaks must be repaired within 30 days (120 with an industrial process shutdown).
- When a chiller is pressurized above atmosphere, a leak pushes refrigerant out.
3 sample questions
Verified practice questions from this unit.
Question 1. Most of a running low-pressure chiller is below atmospheric pressure. What happens when it has a leak?
- ① The chiller pressure rises above 100 psig
- ② Air and moisture leak into the system
- ③ Refrigerant sprays out of the leak at high pressure
- ④ Nothing, because low-pressure systems cannot leak
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Answer: ② Air and moisture leak into the system
Key point: Low-pressure leaks pull air and moisture in
Because much of a low-pressure system runs below atmospheric pressure (in a vacuum), a leak lets air and moisture enter the system. These noncondensables collect in the condenser and must be removed by the purge unit.
Wrong choices
- The chiller pressure rises above 100 psig: A leak does not raise pressure that high.
- Refrigerant sprays out of the leak at high pressure: Parts of the system below atmospheric pressure draw air in rather than pushing refrigerant out.
- Nothing, because low-pressure systems cannot leak: Low-pressure systems can and do leak.
Question 2. A comfort cooling chiller holds 900 pounds of R-123. Above what annual leak rate must the owner repair the leaks?
- ① 15 percent
- ② 20 percent
- ③ 10 percent
- ④ 30 percent
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Answer: ③ 10 percent
Key point: Comfort cooling chiller (HCFC): 10%
R-123 is an HCFC, so this chiller falls under 40 CFR 82.157. For comfort cooling appliances with 50 or more pounds, the leak repair trigger is 10 percent per year.
Wrong choices
- 15 percent: 15 percent was an older comfort cooling trigger.
- 20 percent: 20 percent is the trigger for commercial refrigeration.
- 30 percent: 30 percent is the trigger for industrial process refrigeration.
Question 3. What is the highest pressure normally used to leak test a low-pressure centrifugal chiller?
- ① 10 psig
- ② 100 psig
- ③ 1 psig
- ④ 50 psig
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Answer: ① 10 psig
Key point: Low-pressure chiller leak test: 10 psig max
The rupture disc on a low-pressure chiller's evaporator is usually set at 15 psig, so leak test pressure should not exceed 10 psig to avoid bursting it.
Wrong choices
- 100 psig: 100 psig is far too high for a low-pressure chiller.
- 1 psig: 1 psig is lower than needed; the usual maximum is 10 psig.
- 50 psig: 50 psig would burst the rupture disc.
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