Type III: Low-pressure

Study guide

License Method EPA 608 prep. This guide was checked against the eCFR (40 CFR Part 82 Subpart F and Part 84 Subparts B and C) as of October 2026. Rules that changed recently are marked NEW or CHANGED.

What Type III covers

A Type III certification lets you maintain, service, repair, or dispose of low-pressure appliances. In practice, that mostly means centrifugal chillers in large buildings, campuses, hospitals, and plants. (40 CFR 82.161(a)(1)(iii))

On the exam, the Type III section is 25 questions, given closed-book and proctored. You need 70%, which works out to 18 of 25 correct. Pass Core, Type I, Type II, and Type III and you're Universal. (Appendix D to Subpart F)

What makes an appliance "low-pressure"

A low-pressure appliance uses a refrigerant whose liquid-phase saturation pressure is below 45 psia at 104 °F. (82.152) EPA's examples are R-11, R-123, R-113, and R-245fa. Newer low-GWP chillers use refrigerants like R-1233zd(E) (GWP 4) and R-514A (GWP 3), which also run at low pressure.

The key physical fact: most of a low-pressure system runs below atmospheric pressure. The evaporator always does, and at normal room temperatures an idle R-11 or R-123 machine can sit slightly below atmospheric too. When a low-pressure system leaks, air and moisture leak in, and refrigerant doesn't leak out. That's the reason for the purge unit, the special leak-test methods, and the water-freezing warnings below.

Boiling points at atmospheric pressure (helpful for the 85 °F rule below): R-11 is about 75 °F, R-123 about 82 °F, and R-113 about 118 °F.

Required evacuation level

(40 CFR 82.156, Table 1)

• 25 mm Hg absolute is close to a perfect vacuum. Standard atmosphere is 760 mm Hg (29.92 in. Hg, 14.7 psia), so 25 mm Hg absolute works out to about 29 in. Hg vacuum. (1 in. Hg is 25.4 mm Hg.)
• CHANGED: Older study materials listed 25 in. Hg vacuum for pre-1993 recovery machines and broke low-pressure systems out by size (under or over 200 lb). The current Table 1 has a single row for low-pressure appliances: 25 mm Hg absolute no matter when the machine was made or how big the charge is. If an exam item still tests the old split, the 200-lb line and the 1993 date are what it's probing. Know both, but the current regulation is what you answer to in the field.
• Before opening the system, you must verify the level has been reached.
• After you reach 25 mm Hg, wait a few minutes. If the pressure rises, liquid refrigerant or refrigerant dissolved in the oil is still boiling off. Keep recovering.

Exceptions

1. Non-major repair, with no evacuation to the atmosphere afterward: pressurize a low-pressure appliance up to 0 psig, that is, to atmospheric pressure, before you open it. Cover any openings where the work can't be isolated. (82.156(a)(1)(ii))
   • The 85 °F rule. For refrigerants that boil at or below 85 °F at atmospheric pressure (R-11, R-123), you may not use nitrogen or any other method that requires purging afterward. For refrigerants that boil above 85 °F (R-113), use heat to raise the pressure as far as you can, and then you may finish with nitrogen up to atmospheric.
   • Approved ways to raise the pressure: controlled hot water run through the tubes, or a built-in system heating/pressurization device such as a Prevac.
2. Oil changes: evacuate or pressurize the appliance (or the isolated section) to 5 psig or lower before opening, or drain the oil into a system receiver at 5 psig or lower. Heat the oil to about 130 °F before removing it so the dissolved refrigerant boils out. (82.156(a)(1)(iii); EPA Test Topics)
3. Leaky appliance: isolate the leaking components. Take the non-leaking parts to 25 mm Hg absolute, and take the leaking parts to the lowest level you can reach without contaminating the refrigerant, never higher than 0 psig. (82.156(a)(2))

Major repair means removing the compressor, condenser, evaporator, or an auxiliary heat-exchange coil, or uncovering an opening of more than 4 square inches of flow area for more than 15 minutes. Anything else is non-major. (82.152)

Recovery techniques for low-pressure chillers

• Remove the liquid first, then the vapor. Liquid comes out fast. Chiller shells are huge, so a large amount of refrigerant is still present as vapor after the liquid is gone, and vapor recovery takes most of the job's time.
• Keep the water moving. During evacuation, the refrigerant boils at very low temperatures and can freeze the water in the tubes, which cracks them. Circulate water through the evaporator and condenser tubes, or drain them, while recovering. Typically the chilled-water and condenser-water pumps run, along with the recovery unit's condenser water.
• Suspect a tube leak? Drain the water side before recovery so water isn't pulled into the refrigerant circuit when the vessel goes into vacuum.
• Many low-pressure recovery machines have a water-cooled condenser. Their high-pressure cut-out is typically set around 10 psig, and the rupture disc on a low-pressure recovery vessel relieves at 15 psig.
• Use certified recovery equipment. Pre-Nov 15, 1993 machines must still reach 25 mm Hg absolute to count as certified. Use it according to the manufacturer's instructions.
• Never mix refrigerants (R-11 and R-123, for example). Use dedicated, labeled containers.
• Refrigerant can go back into the same chiller or another chiller owned by the same owner without reclaiming it. If it goes to a new owner, it must be reclaimed to AHRI 700 by an EPA-certified reclaimer. Knowingly releasing refrigerant after recovering it is a venting violation. (82.154, 82.156(h))

Leak detection on low-pressure systems

Signs of a leak: the purge unit runs too often or discharges too much, there's moisture in the refrigerant, and air is in the system (high condensing pressure). A tube leak lets water into the refrigerant side.

Leak-test pressurization, in EPA's order of preference:

1. Hot water run through the tubes, or a built-in heating/pressurization device (Prevac)
2. Nitrogen

Maximum leak-test pressure is 10 psig. The chiller's rupture disc sits on the evaporator, typically opens at 15 psig, and should be piped outdoors. Pressurize above 10 psig and you risk blowing the disc and losing the charge.

Other methods:

• A hydrostatic tube test finds leaks in the water tubes of the evaporator and condenser.
• A standing vacuum ("time-to-rise") test on an empty, evacuated machine shows whether it's tight but doesn't locate the leak. Use it with a method that does, such as an electronic detector, ultrasonic, bubbles, or dye. (Leak inspection definition, 82.152 and 84.102)
• Leak inspections must cover every visible, accessible component. You can skip parts that are insulated, under ice, underground, behind walls, more than 2 m above a support surface, or unsafe.

The purge unit

Air and moisture leak into a low-pressure machine because it runs in a vacuum. These non-condensables collect at the top of the condenser. They raise head pressure, waste energy, and moisture forms acid. The purge unit draws from the top of the condenser, separates the non-condensables from the refrigerant, returns the refrigerant, and vents the air.

• High-efficiency purge units release very little refrigerant per pound of air removed.
• Purge run time is a leak indicator. If it climbs, find and fix the leaks.
• Refrigerant that the purge discharges counts toward the leak rate, unless it's captured and destroyed at 98% efficiency or better. (82.157(k), 84.106(k))

Recharging a low-pressure chiller

• After evacuating, charge vapor first. Liquid hitting a deep vacuum boils instantly and gets extremely cold, cold enough to freeze water in the tubes. Keep charging vapor until the system pressure corresponds to a saturation temperature above freezing (32 °F). Then switch to liquid.
• Charge through the evaporator charging valve, which is the lowest access point on the machine.
• Keep water flowing through the tubes while charging.
• Never energize the compressor motor while the machine is under a deep vacuum, because of motor winding damage.

Leak repair rules for chillers

Low-pressure chillers fall under two leak-repair programs, depending on the refrigerant. The AIM Act program for HFCs is a separate rule from Section 608 (40 CFR 84.106). You need it on the job, but testing programs may not test it yet.

Even when no leak-repair rule applies, the venting ban, certified recovery, evacuation levels, technician certification, and sales restriction still apply to every non-exempt refrigerant.

Thresholds (same in both programs):

• Comfort cooling: 10%. Most building chillers fall here.
• Commercial refrigeration: 20%
• Industrial process refrigeration: 30%

Timeline

• Repair within 30 days of the addition that showed the chiller over its threshold. IPR gets 120 days if an industrial process shutdown is needed.
• A certified technician does the leak inspection that locates the leaks.
• Initial verification test after the repair, before adding refrigerant. Follow-up verification test within 10 days.
• Extension when parts are unavailable: up to 30 days after they arrive, capped at 180 days (270 for IPR shutdowns).
• If repairs fail or the owner decides not to repair: a retrofit or retirement plan within 30 days, signed, dated, and kept on site, with the work completed within 1 year. Any request for more time goes in within 7 months.
• Leak inspections after an exceedance: annually for comfort cooling until there's one year under the threshold. Commercial refrigeration and IPR systems of 500 lb or more get quarterly inspections until there are four quarters in a row under the threshold.
• Chronic leaker: an appliance that leaks 125% or more of its full charge in a calendar year must be reported to EPA by March 1.
• Mothballing, meaning evacuating to at least atmospheric and shutting down, pauses the clocks until refrigerant is added again.

Leak-rate math (practice)

• Annualizing: you add 30 lb to a 600-lb chiller 90 days after the last addition. That's (30/600) ÷ (90/365) = 0.05 ÷ 0.247, or about 20%, which is over the 10% comfort-cooling threshold.
• Rolling average: an 800-lb chiller received 60 lb over the past 365 days. 60/800 = 7.5%, which is under 10%.
• Every appliance at the facility must use the same method. Calculate every time refrigerant is added.

Records: keep leak-repair records for 3 years, and full-charge records until 3 years after the chiller is retired. The technician gives the owner documentation of the amount and type of refrigerant added.

Refrigerant phaseouts that affect chillers

• R-11 is a CFC. U.S. production of CFCs ended January 1, 1996.
• R-123 is an HCFC (Class II ODS). All HCFC production and import ends in 2030. After that, R-123 chillers will be serviced with recovered and reclaimed refrigerant.
• AIM Act technology transitions: new comfort-cooling chillers made or installed from Jan 1, 2025 must use refrigerant with a GWP under 700. That rules out R-134a (1,430) for new comfort chillers. R-1233zd(E), R-514A, and R-513A (630) all qualify. (40 CFR 84.54) This is a separate rule from Section 608 (40 CFR 84.54). You need it on the job, but testing programs may not test it yet.

Safety in the chiller room

• ASHRAE Standard 15 governs machinery rooms: refrigerant detectors and alarms, mechanical ventilation, and relief piping vented outdoors. EPA's test topics specifically call out an oxygen-deprivation sensor (required with all refrigerants) and a refrigerant sensor/monitor in the equipment room for R-123.
• R-123 is ASHRAE safety class B1: higher toxicity, no flame propagation. Keep exposure low and fix leaks quickly. R-1233zd(E) is A1.
• Refrigerant vapor is heavier than air, so it collects low and displaces oxygen. Use SCBA for large releases.
• An open flame or hot surface decomposes refrigerant into toxic acids (HCl and HF, plus phosgene from chlorinated refrigerants).
• Wear safety glasses and gloves. Liquid refrigerant causes frostbite.

Rapid-fire numbers to memorize