24 Type III — Low-Pressure Practice Questions & Answers

1. 1. A centrifugal chiller charged with R-123 is being opened so its compressor can be replaced. To what level must the appliance be evacuated before the compressor is removed?

   • A.10 in. Hg vacuum
   • B.25 in. Hg vacuum
   • C.100 mm Hg absolute
   • D.25 mm Hg absolute✓ Answer

   Removing the compressor is a major repair, and 40 CFR 82.156 sets a single evacuation requirement for low-pressure appliances: 25 mm Hg absolute (roughly 29 in. Hg of vacuum). Only a vacuum that deep will boil the remaining low-pressure refrigerant out of the oil and out of the machine's shells before it is opened to the atmosphere.

   Source: 40 CFR 82.156(a) evacuation requirements table (low-pressure appliances); "major maintenance, service, or repair" defined at 40 CFR 82.152Report a problem with this question

2. 2. A technician's low-pressure recovery machine was manufactured in 1991, and the chiller being serviced holds a 900 lb charge of R-11. How does this affect the required evacuation level?

   • A.Pre-1993 equipment need only reach 15 in. Hg
   • B.Pre-1993 recovery equipment is for disposal only
   • C.It does not — 25 mm Hg absolute always applies✓ Answer
   • D.Charges over 200 lb require a deeper vacuum

   The sliding scale that varies with charge size and with the November 15, 1993 manufacturing date applies to high- and very-high-pressure appliances. Low-pressure appliances have one fixed requirement — 25 mm Hg absolute — because the refrigerant's very low saturation pressure means nothing less will remove it from the machine.

   Source: 40 CFR 82.156(a) evacuation requirements table — low-pressure appliance row has no charge-size or pre/post-November 15, 1993 distinctionReport a problem with this question

3. 3. Before opening a low-pressure chiller for work that is NOT a major repair and NOT an oil change, what is the highest pressure to which the regulation allows the appliance to be evacuated or pressurized?

   • A.10 psig
   • B.0 psig✓ Answer
   • C.5 psig
   • D.15 psig

   For a non-major repair 82.156(a)(1)(ii) accepts atmospheric pressure — no higher than 0 psig — because at 0 psig there is no positive pressure to drive refrigerant out of the opening. Anything above atmospheric would push refrigerant into the machinery room when the machine is broken into. Oil changes are the one carve-out, at 5 psig under (a)(1)(iii).

   Source: 40 CFR 82.156(a) — non-major repair provision for low-pressure appliancesReport a problem with this question

4. 4. A technician needs only to change the oil in a low-pressure chiller. Under the evacuation rules, what is the highest pressure the appliance may be raised to before the oil is drained?

   • A.0 psig
   • B.10 psig
   • C.15 psig
   • D.5 psig✓ Answer

   An oil change alone gets a narrow allowance of up to 5 psig, slightly above the 0 psig limit that applies to other non-major work, because a small positive pressure helps push the oil out of the sump. It is still far below the 15 psig rupture-disc setting.

   Source: 40 CFR 82.156(a) — 5 psig allowance for oil changes on low-pressure appliancesReport a problem with this question

5. 5. Which of the following counts as a "major" maintenance, service, or repair on a low-pressure appliance?

   • A.Changing the compressor oil
   • B.Replacing a purge filter
   • C.Replacing a pressure gauge
   • D.Removing the evaporator✓ Answer

   A major repair is defined as removal of the compressor, condenser, evaporator, or auxiliary heat exchange coil. These components hold the bulk of the charge, so opening them without a full 25 mm Hg absolute evacuation would release a large quantity of refrigerant.

   Source: 40 CFR 82.152 — definition of "major maintenance, service, or repair"Report a problem with this question

6. 6. An R-123 chiller must have its internal pressure raised to atmospheric so it can be opened for service. Which method does the regulation permit?

   • A.Dry nitrogen from a regulated cylinder
   • B.Controlled hot water through the tubes✓ Answer
   • C.Compressed air from the shop air supply
   • D.Oxygen from a welding gas cylinder

   R-123 boils at about 82.2°F, at or below the 85°F cutoff in the rule, so methods that require subsequent purging — nitrogen or any other inert gas — are prohibited, since purging that gas out later would also vent refrigerant. Heat raises the pressure using the charge itself and leaves no non-condensable behind. (Nitrogen up to 10 psig is still acceptable for leak testing, which is a separate rule.)

   Source: 40 CFR 82.156(a) — pressurization restriction for refrigerants boiling at or below 85°F at atmospheric pressureReport a problem with this question

7. 7. A low-pressure appliance leaks so badly that the recovery equipment cannot pull it down to 25 mm Hg absolute. What does the regulation require the technician to do?

   • A.Vent the remaining charge and log the release
   • B.Pressurize with nitrogen to 10 psig and open
   • C.Nothing — the leaky-appliance exception waives it
   • D.Evacuate as low as is attainable, not above 0 psig✓ Answer

   The leaky-appliance exception relaxes the number but never permits venting: pulling harder on a badly leaking machine only draws in air and moisture that contaminate the recovered refrigerant, so the rule caps the effort at the lowest level attainable and no higher than 0 psig.

   Source: 40 CFR 82.156(i) — leaky appliance exception, not to exceed 0 psigReport a problem with this question

8. 8. After a low-pressure chiller reaches 25 mm Hg absolute, the technician isolates it from the recovery unit and watches the gauge. The pressure begins to climb. What does that indicate?

   • A.The vacuum pump oil has become saturated with moisture
   • B.Evacuation is not done — vapor is still coming off✓ Answer
   • C.The recovery machine is oversized for the appliance
   • D.Nothing unusual — a rise after isolation is normal

   This standing-vacuum (pressure-rise) check is how the required level is confirmed. A rise means either trapped refrigerant and moisture are still vaporizing or ambient air is being drawn in through a leak; either way the appliance has not truly been evacuated and must be pumped down again.

   Source: 40 CFR 82.156(a) — required evacuation level must be achieved and verified; standing vacuum (pressure-rise) practiceReport a problem with this question

9. 9. What is the maximum pressure to which a low-pressure centrifugal chiller should be raised while leak testing it?

   • A.5 psig
   • B.25 psig
   • C.10 psig✓ Answer
   • D.15 psig

   The rupture disc on a low-pressure chiller is set to burst at 15 psig, and a burst disc dumps the entire charge to the atmosphere. Stopping at 10 psig leaves a deliberate safety margin below the relief setting, so the machine can never be pressure-tested above its own relief device.

   Source: 40 CFR 82.156 leak-test practice; ASHRAE 15 pressure-relief (rupture disc) setting of 15 psig on low-pressure chillersReport a problem with this question

10. 10. Which is the preferred first choice for raising the pressure inside a low-pressure chiller in order to leak test it?

    • A.Hot water circulated through the tubes✓ Answer
    • B.Oxygen drawn from a welding cylinder
    • C.Dry nitrogen from a regulated cylinder
    • D.Compressed air from the shop air supply

    Heating the charge raises pressure using the refrigerant already in the machine, so no non-condensable gas is added and nothing has to be purged out afterward. Regulated nitrogen is the accepted second choice; oxygen must never be used because it can react violently with refrigerant oil, and compressed air carries moisture into the system.

    Source: EPA Section 608 Type III test topics — leak detection on low-pressure appliances; 40 CFR 82.156 pressurization methodsReport a problem with this question

11. 11. A building's R-123 chiller shows no oil traces around the joints and no measurable loss of charge, but the purge unit now runs almost continuously. What is the most likely explanation?

    • A.The condenser water temperature is low
    • B.A leak is drawing air and moisture inside✓ Answer
    • C.The chiller has been badly overcharged
    • D.The purge unit's compressor is oversized

    Because the low side of a low-pressure machine runs in a vacuum, a leak admits air rather than releasing refrigerant, so the classic clues of oil traces and a falling charge are absent. The purge unit's job is to remove that in-leaking air, so excessive purge run time is the tell-tale symptom of a leak.

    Source: EPA Section 608 Type III test topics — leak detection; purge unit operation on low-pressure appliancesReport a problem with this question

12. 12. Why does a leak on the low side of an operating low-pressure chiller pull air and moisture into the machine rather than losing refrigerant?

    • A.The float device seals leaks from the inside
    • B.The low side runs below atmospheric pressure✓ Answer
    • C.Refrigerant is heavier than air and settles low
    • D.The purge unit holds the shells above 0 psig

    Low-pressure refrigerants such as R-11, R-123 and R-113 have saturation pressures below atmospheric at normal evaporator temperatures, so the evaporator runs in inches of mercury of vacuum. Flow always goes from higher to lower pressure, and here the higher pressure is outside the machine.

    Source: 40 CFR 82.152 low-pressure appliance definition; EPA Section 608 Type III test topics — refrigeration fundamentalsReport a problem with this question

13. 13. Why should nitrogen never be added to a low-pressure chiller that is still holding its full refrigerant charge?

    • A.Its added partial pressure can burst the rupture disc✓ Answer
    • B.It freezes water standing in the evaporator tubes
    • C.It reacts chemically with R-123 to form acids
    • D.It dissolves in the oil and cannot be removed

    By Dalton's law the total pressure in the shell is the refrigerant's saturation pressure plus the partial pressure of the added nitrogen, so a machine that seemed to be well below 15 psig can cross the rupture-disc setting quickly. If the disc lets go, the entire charge is released.

    Source: ASHRAE 15 rupture-disc setting (15 psig) on low-pressure chillers; Dalton's law of partial pressuresReport a problem with this question

14. 14. A 900 lb charge of R-123 serves a centrifugal chiller used for building comfort cooling. What annual leak rate triggers the Section 608 leak-repair requirements for this appliance?

    • A.15%
    • B.10%✓ Answer
    • C.20%
    • D.35%

    Comfort cooling and "all other" appliances with a full charge of 50 or more pounds of an ozone-depleting refrigerant have a 10% trigger rate, measured as a percentage of full charge lost over a 12-month period. Commercial refrigeration is 20% and industrial process refrigeration is 30%; the older 15% and 35% figures were superseded.

    Source: 40 CFR 82.157 — leak repair trigger rates for appliances with a full charge of 50 or more poundsReport a problem with this question

15. 15. For an industrial process refrigeration appliance containing 50 or more pounds of an ozone-depleting refrigerant, the leak-repair requirements are triggered at an annual leak rate of:

    • A.10%
    • B.20%
    • C.30%✓ Answer
    • D.35%

    Industrial process refrigeration carries the highest allowance, 30%, because these systems are large and hard to isolate — but the pre-2019 figure of 35% still printed in many study guides is no longer the standard. The rate is computed as the percentage of full charge lost over a 12-month period.

    Source: 40 CFR 82.157 — 30% trigger rate for industrial process refrigerationReport a problem with this question

16. 16. A low-pressure chiller subject to the leak-repair rule is found to be leaking above its trigger rate. What is the owner/operator required to do?

    • A.Recover the charge at once and retire the appliance
    • B.Repair the leaks by the next quarterly check
    • C.Repair the leaks within 30 days of discovery✓ Answer
    • D.Repair the leaks within 90 days of discovery

    The rule gives the owner a choice but puts both paths on a 30-day clock from discovery: fix the leaks, or commit in writing to retrofitting or retiring the appliance and finish that work within one year. Industrial process shutdowns may receive additional time, up to 120 days.

    Source: 40 CFR 82.157 — 30-day repair requirement and retrofit/retirement plan optionReport a problem with this question

17. 17. What is the correct order for removing refrigerant from a low-pressure chiller?

    • A.Recover the vapor first, then the liquid
    • B.Recover the liquid only — vapor is not required
    • C.Recover vapor only, to avoid freezing the tubes
    • D.Recover the liquid first, then the vapor✓ Answer

    Liquid is recovered first because a pound of liquid moves through the recovery machine far faster than a pound of vapor, which greatly shortens the job. Recovery is not complete until the remaining vapor is also pulled down to the required 25 mm Hg absolute.

    Source: EPA Section 608 Type III test topics — recovery techniques; 40 CFR 82.156(a) required evacuation levelReport a problem with this question

18. 18. Before draining the oil from a low-pressure chiller, the oil should be heated to approximately what temperature?

    • A.130°F✓ Answer
    • B.212°F
    • C.100°F
    • D.185°F

    Low-pressure refrigerant dissolves readily in the oil, and warming the oil to about 130°F drives that refrigerant out so the recovery system captures it instead of losing it to the room when the sump is drained. The oil must not be overheated, since excessive temperature breaks the refrigerant down.

    Source: EPA Section 608 Type III test topics — recovery techniques, oil removal from low-pressure appliancesReport a problem with this question

19. 19. While a low-pressure chiller is being evacuated for service, why must chilled water be kept circulating through the evaporator tubes (or the water drained out)?

    • A.Circulating water keeps the purge unit from short-cycling
    • B.Boiling refrigerant can freeze standing water✓ Answer
    • C.Water flow makes the recovery machine faster
    • D.Water flow keeps the rupture disc from bursting

    Pulling the machine toward 25 mm Hg absolute lowers the refrigerant's saturation temperature far below 32°F, and the heat to boil it off comes out of the water in the tubes. Moving water carries in enough heat to stay liquid; standing water freezes, expands and ruptures the tube bundle.

    Source: EPA Section 608 Type III test topics — recovery techniques, protecting evaporator tubes during evacuationReport a problem with this question

20. 20. An evacuated low-pressure chiller is being recharged. Why is vapor introduced before liquid?

    • A.Liquid refrigerant would damage the purge unit
    • B.Vapor charging is faster than liquid charging
    • C.Vapor charging strips non-condensables from the drum
    • D.Liquid flashing in a deep vacuum freezes the tubes✓ Answer

    Vapor is added until the system pressure corresponds to a saturation temperature above the freezing point of water — roughly 36°F — and only then is liquid admitted. Note the deliberate inversion test-takers miss: you RECOVER liquid first, but you CHARGE vapor first.

    Source: EPA Section 608 Type III test topics — recharging techniques for low-pressure appliancesReport a problem with this question

21. 21. On a centrifugal chiller, liquid refrigerant is normally charged into the machine through:

    • A.The evaporator charging valve✓ Answer
    • B.The compressor suction port
    • C.The condenser relief fitting
    • D.The purge unit's outlet port

    The float or orifice metering device only meters liquid flowing from the condenser down to the evaporator, so charging at the evaporator's low-side valve puts the liquid directly into the shell where it belongs, below the tube bundle, instead of slugging it back through the compressor or the metering device.

    Source: EPA Section 608 Type III test topics — recharging techniques; centrifugal chiller float/orifice meteringReport a problem with this question

22. 22. Which characteristic defines a "low-pressure appliance" in the Section 608 regulations?

    • A.A hermetically sealed compressor
    • B.A refrigerant at 45-170 psia at 104°F
    • C.A full charge of less than 50 pounds
    • D.A refrigerant below 45 psia at 104°F✓ Answer

    The class is defined by the refrigerant's pressure, not by the size or charge of the machine: below 45 psia at 104°F is low-pressure (R-11, R-123, R-113, R-245fa), 45-170 psia is medium-pressure and 170-355 psia is high-pressure. That very low saturation pressure is exactly why these machines run in a vacuum on the low side.

    Source: 40 CFR 82.152 — definition of "low-pressure appliance"Report a problem with this question

23. 23. What does the purge unit on a low-pressure chiller do, and where does it draw from?

    • A.Removes non-condensable gas from the top of the condenser✓ Answer
    • B.Adds nitrogen to keep the low side above atmospheric
    • C.Removes excess refrigerant from the evaporator bottom
    • D.Removes oil from the refrigerant at the compressor sump

    Air drawn in through the sub-atmospheric low side does not condense, so it migrates to and collects at the high point of the condenser, where it raises head pressure and cuts capacity. The purge unit pulls from that point, separates the refrigerant it carries along, and discharges the air and any moisture with it.

    Source: EPA Section 608 Type III test topics — refrigeration fundamentals, purge unit operationReport a problem with this question

24. 24. Under ASHRAE Standard 15, what refrigerant-detection equipment must a machinery room housing an R-123 chiller have?

    • A.An oxygen deprivation sensor by itself
    • B.A combustible-gas detector for R-123 vapor
    • C.An oxygen sensor plus an R-123 monitor✓ Answer
    • D.A refrigerant vapor monitor by itself

    An oxygen deprivation sensor is required for every refrigerant so the room stays at or above 19.5% oxygen, but R-123 is a higher-toxicity B1 refrigerant whose occupational exposure limit is reached long before oxygen is meaningfully displaced. A dedicated monitor is therefore needed to alarm at that exposure limit; on alarm the room is evacuated and re-entry requires SCBA.

    Source: ASHRAE Standard 15 — machinery room refrigerant detection and oxygen deprivation sensing; EPA Section 608 Type III safety topicsReport a problem with this question

Practice questions modeled on the EPA Section 608 Technician Certification content (Clean Air Act §608; 40 CFR Part 82). Not affiliated with or endorsed by the U.S. Environmental Protection Agency or any approved certifying organization. Study the official EPA program materials before testing. Official EPA 608 →