EPA 608 Type III Practice Test: Real Questions & Answers (Low-Pressure Chillers)

Correct answer: B. Refrigerants with boiling point ABOVE 50°F at atmospheric pressure

Low-pressure refrigerants have boiling points above 50°F at atmospheric pressure (R-11, R-123, R-245fa, R-1233zd). At normal temperatures, they are partially vapor; the system must operate in vacuum to condense them.

Correct answer: C. Centrifugal chillers using R-123

Type III covers low-pressure appliances — primarily large centrifugal chillers (water-cooled) using R-11, R-123, R-245fa, or R-1233zd. Residential AC, RTUs, and walk-ins are Type II (high-pressure).

Correct answer: B. Because low-pressure refrigerants have boiling points ABOVE 50°F at atmospheric pressure, so the saturation pressure at typical evaporator temperatures (~40°F) is below atmospheric

Boiling point above 50°F at 1 atm means saturation pressure at typical chiller evaporator temps (~40°F) is below 1 atm — sub-atmospheric. Creates the air-infiltration / non-condensable accumulation challenge unique to Type III.

Correct answer: C. 25 mm Hg absolute

Per 40 CFR 82.156: low-pressure appliances require evacuation to 25 mm Hg absolute (≈29 in Hg vacuum) with post-1993 equipment — the deepest evacuation of any appliance class. Critical Type III question.

Reference: 40 CFR 82.156, Appendix B

Correct answer: A. 25 mm Hg absolute

Pre-1993 equipment on low-pressure appliances must achieve 25 mm Hg absolute — SAME as post-1993. Type III is the only category where pre/post-1993 evacuation requirements are identical. The 5 psig exception applies only during oil change with the compressor running.

Reference: 40 CFR 82.156, Appendix B

Correct answer: C. 5 psig

82.156 provides an exception during oil changes performed with the compressor running: the appliance may be pressurized up to 5 psig. Normal recovery requires 25 mm Hg absolute, but this isn't practical during running oil changes.

Reference: 40 CFR 82.156

Correct answer: B. Remove non-condensable gases (primarily air and water vapor) that infiltrate the sub-atmospheric system

Purge units remove non-condensable gases (air, water vapor) that infiltrate through leaks in sub-atmospheric systems. Non-condensables raise discharge pressure, reduce capacity, and waste energy. Purge units are UNIQUE to low-pressure systems.

Correct answer: B. Top of the condenser

Non-condensables accumulate at the top of the condenser (lower density than refrigerant vapor). Purge units draw from there to capture and remove them.

Correct answer: B. Refrigerant loss while removing non-condensables

High-efficiency purge units separate refrigerant vapor from non-condensables, returning the refrigerant to the system and venting only the non-condensables. Older purges vented both, causing significant refrigerant loss.

Correct answer: B. The chiller likely has a leak allowing air to infiltrate the sub-atmospheric portion of the system

Excessive purge cycling indicates air infiltration, which means there's a LEAK on the sub-atmospheric (low) side. Counter-intuitive: leaks in low-pressure systems pull AIR IN (not refrigerant out). Excessive purging = leak indicator.

Correct answer: B. The system operates in vacuum on the low side, so air leaks IN rather than refrigerant leaking OUT — standard sniff tests at atmospheric conditions won't find them

Low-pressure systems pull air IN through leaks (not refrigerant out). Standard electronic detectors that sniff for refrigerant won't find a leak unless the system is pressurized above atmospheric. Type III leak detection often requires pressurizing the system.

Correct answer: B. 10 psig (limited by the rupture disc setting)

Pressurizing for leak testing must stay below the rupture disc pressure (typically 15 psig). Standard practice limits test pressure to 10 psig with dry nitrogen — only slight pressurization is needed to bring the system above atmospheric so leaks become detectable.

Correct answer: B. Provides emergency pressure relief if system pressure rises above design limits — protects equipment designed for sub-atmospheric operation

Rupture discs are emergency pressure-relief devices. Low-pressure chillers are designed for sub-atmospheric operation — high pressure (e.g., from fire) could rupture the vessel. The disc breaks at ~15 psig to relieve pressure before catastrophic failure.

Correct answer: B. 15 psig

Rupture discs on low-pressure systems are typically set at 15 psig per ASHRAE standards. Pressurizing beyond this could rupture the disc and release the entire refrigerant charge.

Correct answer: B. Replace the rupture disc — they are one-time-use devices

Rupture discs are ONE-TIME-USE — they physically rupture (break open) to relieve pressure. Once activated, the disc must be physically replaced. The chiller must also be inspected for the cause of the over-pressure event.

Correct answer: B. Their boiling points at atmospheric pressure are above typical room temperatures (R-123 BP ≈ 82°F), so at normal room temp and 1 atm they exist as liquid that wants to vaporize

R-123's BP at 1 atm is ~82°F. At room temp (68–77°F) and atmospheric pressure, R-123 is at saturation conditions — readily vaporizes. Why low-pressure chillers must run in vacuum to maintain liquid refrigerant at typical chiller temperatures.

Correct answer: B. The system must be pulled to a much deeper vacuum (25 mm Hg absolute), and the low operating pressure creates a small pressure differential into the recovery vessel

Recovery requires pulling to 25 mm Hg absolute — much deeper than high-pressure. Small pressure differential between sub-atmospheric refrigerant and recovery vessel makes the process slow. Heating the chiller barrel (warm water circulation) is often required.

Correct answer: B. Prevents ice formation that could damage tubes; maintains adequate refrigerant pressure for transfer; speeds recovery

During recovery, the chiller barrel cools dramatically. Without warm water circulation, residual moisture can freeze and damage tubes. Warm water also keeps refrigerant pressure high enough for efficient transfer.

Correct answer: B. Ice can form in the tube bundle and freeze/damage the tubes — saturation temperature of residual water drops to freezing under deep vacuum

Deep vacuum drops the saturation temperature of any residual water to freezing. Ice formation expands and can damage tubes. Preventive: keep warm water circulating to maintain tube-metal temperatures above 32°F.

Correct answer: C. 82°F (just above room temperature)

R-123 BP ≈ 82°F at 1 atm. At typical room temp (68–77°F), R-123 vapor pressure is just below atmospheric — must operate in slight vacuum to condense. PT chart for R-123 shows vacuum at typical chiller temps.

Correct answer: B. B1 — higher toxicity, lower flammability; equipment rooms require refrigerant detectors and alarms, technicians use respiratory protection when concentrations may be elevated

R-123 is B1: 'B' = higher toxicity (effects below 400 ppm); '1' = no significant flammability. Triggers ASHRAE 15 requirements for machinery rooms: detectors with alarms, ventilation, emergency shutdown. Differs from newer R-1233zd (A1).

Correct answer: C. A1 — non-toxic and non-flammable; a significant safety improvement over R-123's B1

R-1233zd(E) is A1 — safest classification, neither significant toxicity nor flammability. Major safety improvement over R-123 (B1). Still operates sub-atmospheric like R-123, so Type III certification and techniques apply.

Correct answer: B. Electronic refrigerant detectors and audible/visual alarms that activate when concentrations exceed safe thresholds

ASHRAE Standard 15 requires electronic refrigerant detectors with alarms in machinery rooms housing refrigeration equipment — including B1 refrigerants like R-123. Must trigger at or below the ASHRAE 34 toxicity limit.

Correct answer: C. Ventilate the area, avoid direct skin and eye contact with liquid, use appropriate respiratory protection when concentrations may be elevated

R-123 is B1 (higher toxicity). Safe handling: ventilate area; avoid direct contact with liquid (causes irritation, frostbite); use respiratory protection when vapor concentrations may be elevated. Not flammable (class 1) — toxicity is the primary concern.

Correct answer: C. Oxygen can combine with compressor oil under pressure to create an explosive mixture — fire and explosion hazard

Oxygen mixed with hydrocarbon-based compressor oil under elevated pressure creates conditions for a violent exothermic reaction — effectively a diesel-cycle explosion inside the refrigerant circuit. Use only DRY NITROGEN for leak testing. On low-pressure systems, limit to 10 psig to protect the rupture disc.

Correct answer: C. Purge unit

Purge unit is unique to low-pressure appliances. Its function (continuously removing non-condensables from sub-atmospheric systems) has no analog in high-pressure systems, which maintain positive pressure and expel refrigerant outward through leaks.

Correct answer: C. 10% of full charge

Current 40 CFR 82.157 sets comfort cooling threshold at 10% per 12-month period. Centrifugal R-123 / R-11 chillers used for HVAC comfort cooling fall in this category. Older materials may cite 15% (pre-2019); current is 10%.

Reference: 40 CFR 82.157

Correct answer: B. Either repair the leak within 30 days of discovery OR develop a written retrofit/retirement plan within 30 days

30-day decision point: either repair within 30 days OR develop a written retrofit/retirement plan within 30 days. If retrofit/retirement: planned action must generally be completed within 1 year. Follow-up verification testing also required.

Reference: 40 CFR 82.157

Correct answer: C. R-11, R-123, R-245fa, and R-1233zd(E)

Low-pressure chillers historically used R-11 (CFC, phased out). R-123 (HCFC) became the standard replacement. R-245fa (HFC) and R-1233zd(E) (HFO) are newer alternatives. R-22, R-410A, R-134a are high-pressure (Type II).

Correct answer: B. Uses high-speed rotating impeller(s) to dynamically compress refrigerant — well-suited to low-pressure refrigerants and large cooling capacities

Centrifugal compressors use high-speed rotating impellers to dynamically compress refrigerant. Well-suited to low-pressure refrigerants (R-123, R-1233zd) and large cooling capacities (200–10,000+ tons). The most common large-tonnage chiller technology.