Type III — low-pressure appliances: practice questions

Correct: D. The low-pressure row is the only one in Table 1 expressed as an absolute pressure rather than a vacuum, and the only one that does not change with the age of the recovery equipment.

• A — The figure is twenty-five millimetres of mercury absolute, not twenty-five inches of vacuum.
• B — Ten inches applies to high-pressure appliances of two hundred pounds or more.
• C — Fifteen inches applies to medium-pressure appliances of two hundred pounds or more.

Correct: A. A low-pressure machine runs below atmospheric pressure, so a leak lets air in rather than letting refrigerant out. The purge unit then works harder removing the non-condensables, which is the signature symptom.

• B — The system sits below atmospheric pressure, so the pressure gradient drives air inward.
• C — Purge units remove non-condensable gases, not surplus refrigerant from an overcharge.
• D — A failed purge unit would show as rising non-condensables, not as increased purging.

Correct: B. Evaporating refrigerant draws its latent heat from whatever is nearest, which is the water in the tubes. Ice expands, and a split tube bundle is an expensive and entirely avoidable failure.

• C — Circulation does not meaningfully raise system pressure or accelerate the recovery.
• D — Sediment is a maintenance concern generally, not the reason for circulating during evacuation.
• A — Purge units operate independently of whether the chiller water is moving.

Correct: C. Heat is preferred because it needs no purging afterwards. Section 82.156(a)(1)(ii) makes the same distinction for non-major repairs, barring methods requiring subsequent purging where the refrigerant boils at or below 85 degrees Fahrenheit.

• D — The order is reversed; nitrogen is the fallback precisely because it must be purged.
• A — Compressed air introduces moisture and is not an approved leak-test pressurisation method.
• B — Oxygen must never be used to pressurise a system containing refrigerant oil.

Correct: D. Liquid refrigerant entering an evacuated chiller flashes to vapour and chills the tubes sharply. Bringing the pressure and temperature up with vapour first removes that freezing risk, and charging goes through the evaporator charging valve.

• A — Non-condensables are removed by the purge unit, not by the order in which you charge.
• B — Valve clearance is confirmed before charging begins and is not the reason for the sequence.
• C — Heating oil to 130 degrees Fahrenheit concerns oil removal, which precedes recharging.