EPA 608 Type III Study Guide: Low-Pressure Chillers, Purge Units and Leak Tests

Why low-pressure chillers behave differently on the EPA 608 test

Type III is the 25-question section for low-pressure appliances: equipment using a refrigerant whose liquid saturation pressure is below 45 psia at 104 °F (40 CFR 82.152). EPA's examples are R-11, R-123, R-113 and R-245fa, and ESCO Institute's 2026 pressure-temperature chart also lists R-1233zd in its low-pressure group. In practice that means centrifugal chillers in large buildings, campuses and plants.

The fact behind most Type III questions is that refrigerants such as R-123 boil near room temperature. On ESCO's 2026 chart, R-123 reads 1.2 inches of mercury vacuum at 80 °F and 0.9 psig at 85 °F, so it crosses atmospheric pressure between those temperatures. At 104 °F it reads only 7.7 psig. Trane's purge manual for R-123 chillers draws the consequence: these chillers "operate with areas of the chiller at less than atmospheric pressure." A leak in a high-pressure system pushes refrigerant out. A leak in the low-pressure parts of a chiller lets air and moisture in.

Purge units and what excessive purging tells you

Air and water vapor that leak in are noncondensables: they collect in the condenser and do not condense with the refrigerant. Trane's manual explains that if they are not removed, the condenser loses efficiency and condenser pressure rises, which lowers the chiller's efficiency and capacity. A purge unit, which Trane says is required on low-pressure centrifugal chillers, is the device that removes them.

That makes the purge a leak indicator, which is how EPA frames it: "signs of leakage into a low-pressure system (e.g., excessive purging)." Trane's CenTraVac manual turns it into a rule of thumb, with a formula for the annual leak rate based on daily purge pump-out time and a chart showing when pump-out times fall in a small-leak or large-leak region. A large-leak reading calls for a thorough leak check right away. Purge questions are a Type III staple, and the 193 Type III questions planned for full EPA 608 prep follow EPA's Type III topics.

Leak testing a low-pressure chiller

To leak-test a chiller you first raise its pressure above atmospheric. EPA's order of preference for low-pressure systems:

1. Controlled hot water, or a built-in heating and pressurization device such as Prevac.
2. Nitrogen, after that.

EPA also lists the "maximum leak test pressure for low-pressure centrifugal chillers" as a topic but does not print the figure on its page. One manufacturer's manual shows why there is a ceiling: Trane's CenTraVac manual says all CenTraVac chillers carry rupture disks that break, releasing refrigerant, if evaporator pressure exceeds 15 psig, and it lists dry nitrogen at 8 psig maximum per machine among installation materials. Those are Trane's figures for Trane equipment; for the figure your test keys, use your certifying program's manual. Trane's manual also warns never to use an open flame to find leaks.

Once a chiller holding an ozone-depleting refrigerant such as R-123 (an HCFC) has a full charge of 50 pounds or more, the Part 82 leak repair rules apply (40 CFR 82.157): 20% for commercial refrigeration, 30% for industrial process refrigeration, and 10% for comfort cooling, which covers most building chillers. Above the trigger, a certified technician locates the leaks and repairs are due within 30 days (120 with an industrial process shutdown), followed by periodic leak inspections, and an appliance leaking 125% of its charge in a calendar year is reported to EPA by March 1. EPA's topic text says "more than 50 pounds," but the rule itself applies at 50 pounds or more. The EPA 608 Type II study guide works through a leak-rate calculation step by step.

Pressurizing for a non-major repair: the 85 °F rule

For a repair that is not major and is not followed by evacuation to the atmosphere, a low-pressure appliance must be pressurized to no higher than 0 psig before it is opened, with openings covered where isolation is not possible (40 CFR 82.156(a)(1)(ii)). How you get there depends on the refrigerant's boiling point at standard atmospheric pressure (29.9 inches of mercury):

EPA's service practice page puts it in one line: methods that require purging, such as nitrogen, "cannot be used except with appliances containing R-113." R-123 fits the first row, since ESCO's chart shows it crossing atmospheric pressure between 80 °F and 85 °F. EPA's Type III topics name the allowed methods for a non-major repair: controlled hot water and a heating or pressurization device such as Prevac. Rules like this, a number tied to a condition, are what the Type III chiller flashcards planned in full EPA 608 prep are for.

Recovering refrigerant from a low-pressure chiller

• Liquid first, then vapor. Recovering liquid at the start speeds the process, but EPA also lists the "need to recover vapor in addition to liquid"
• Evacuate to 25 mm Hg absolute. That is the Table 1 level for low-pressure appliances with recovery equipment of any date (40 CFR 82.156(a)). Converted, 25 mm is about 0.98 inches of mercury absolute, or roughly 28.9 inches of vacuum against the standard 29.9
• Heat the oil to 130 °F before removing it, to minimize refrigerant release from the oil
• Protect the tubes. Circulate or remove the water in the chiller during evacuation, so it does not freeze
• Know the recovery unit's limits. EPA lists the high-pressure cut-out level of recovery devices used with low-pressure appliances; take the figure from your program's manual
• Watch for a rise. After reaching the required vacuum, wait a few minutes. If the pressure rises, refrigerant is still in the system or in the oil

The numbers themselves sit with their conditions in the EPA 608 numbers guide.

Recharging a chiller: vapor before liquid

EPA's recharging topics are short: introduce vapor before liquid to prevent the water in the tubes from freezing, and charge centrifugals through the evaporator charging valve. The chart shows why. A chiller that has just been evacuated sits deep in vacuum, and at those pressures R-123 boils very cold: ESCO's chart puts R-123 at 25.9 inches of vacuum at 0 °F, 20.7 inches at 30 °F and 19.5 inches at 35 °F. Liquid let into the evaporator before the pressure rises past roughly 20 inches of vacuum would boil at or below water's freezing point. Vapor first raises the pressure; liquid follows once boiling can no longer freeze the tubes.

Equipment room safety for EPA 608 Type III

EPA's Type III safety topics cite ASHRAE Standard 15 twice: equipment room requirements, worded as an "oxygen deprivation sensor with all refrigerants," and the need for an equipment room refrigerant sensor for R-123. ESCO's 2026 chart lists R-123 in ASHRAE safety class B1. Arkema's tech tip on ASHRAE Standard 34 codes explains that the number is the flammability class, with 1 meaning no flame propagation, and the letter refers to toxicity.

Two Passy practice questions for EPA 608 Type III

These are original Passy questions, not EPA items.

1. An R-123 chiller needs a non-major repair and will not be evacuated to the atmosphere afterward. How should it reach 0 psig before it is opened?

• A. Use controlled hot water or a heating device such as Prevac to raise the pressure
• B. Add dry nitrogen up to 0 psig, then purge the nitrogen once the repair is finished
• C. Open it while it still sits in deep vacuum, so the refrigerant stays inside the shell
• D. Open it right away, since a low-pressure chiller never rises above 0 psig at all

Answer: A. R-123 boils below 85 °F at standard atmospheric pressure, so 40 CFR 82.156(a)(1)(ii) rules out methods that need purging, such as nitrogen (B). Opening under vacuum draws air and moisture in (C), and D is false: ESCO's chart shows R-123 at 2.5 psig at 90 °F.

2. Why does EPA call for vapor before liquid when recharging an evacuated chiller?

• A. Liquid boiling in deep vacuum can freeze the water in the tubes
• B. Vapor warms the compressor oil to 130 °F before it is drained
• C. Liquid charging first would overload the purge unit's tank
• D. Vapor carries less moisture into the chiller than liquid does

Answer: A. At deep vacuum, R-123 boils below 32 °F on ESCO's chart, so liquid charged too early can freeze the tube water. The 130 °F figure (B) applies to heating oil before removal during recovery, not to recharging.

Studying Type III if chillers are new to you

Type III is the section many candidates have never seen in the field, so learn the one idea first (below-atmospheric operation) and let the rules follow from it: air gets in, purge removes it, pressure must be raised before opening, liquid boils cold in vacuum. Then memorize the figures. The free EPA 608 practice questions include five Type III items, which is a quick way to see whether chillers are new territory, and the EPA 608 study plan lets you weight Type III. When full prep opens, every answer comes with an explanation, and you can see how AI Rescue is planned to re-explain a missed Type III answer in simpler terms.