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35 multiple-choice questions and 17 flashcards on Core — Safety, Leak Detection and Evacuation, about 12% of the HVAC: EPA 608 Tech Cert bank. Every one carries a written rationale.
Core — Safety, Leak Detection and Evacuation is one of 8 chapters in CoStudy's HVAC: EPA 608 Tech Cert bank, and it holds 35 of the bank's 300 multiple-choice questions — roughly 12% of the total. That proportion is not arbitrary: chapters follow the certifying body's published exam outline, and the number of questions in each is set by that domain's published weight, so the share of your practice time this chapter takes matches the share of the real exam it accounts for.
Studying by chapter is worth doing once you have a diagnostic score. A single overall percentage tells you whether you are close; it does not tell you which domain is dragging. Working a weak chapter in isolation, and re-testing it in isolation, is the fastest way to move a score that has stalled — and it is why the mock exams in CoStudy report by domain rather than as one number.
10 questions drawn from this chapter, with the full rationale shown — the controlling principle behind the right answer, and why each wrong option tempts and fails.
An electronic leak detector alarms constantly in a mechanical room. What should the technician do NEXT?
Answer: A — Ventilate the space and re-zero the detector before continuing
A) Correct — a high background concentration saturates the sensor, so clearing the air and resetting the instrument restores useful discrimination. B) hides small leaks that the technician is there to find. C) is a false inference; a saturated sensor alarms everywhere. D) substitutes a less sensitive and more hazardous method.
When evacuating a small appliance prior to recharge, the purpose of pulling deep vacuum is to:
Answer: D — Remove non-condensable gases and moisture before charging
A) Vacuum does not test the compressor. D) Correct — deep vacuum boils off moisture and evacuates non-condensables that would otherwise raise head pressure and form acids. C) Oil return depends on velocity, not vacuum. B) Sanitation is not the goal.
Liquid refrigerant contacting bare skin presents which PRIMARY hazard?
Answer: B — Frostbite from rapid evaporative cooling of the skin
B) Correct — liquid refrigerant flashes to vapor and pulls heat from the skin, producing freeze injury. A) tempts because acids do form inside burned-out systems, but the immediate contact hazard is cold. C) is not the main route of harm; inhalation matters far more than skin absorption. D) is unrelated to refrigerant handling.
Why is triple evacuation used on a system that has been open to atmosphere for an extended period?
Answer: C — It dilutes and removes moisture and noncondensables
C) Correct — breaking the vacuum with dry nitrogen between pulls sweeps out water vapor and noncondensables that a single long pull leaves behind. A) reverses the purpose, since evacuation lowers pressure rather than raising it. B) requires an oil change and a drier, which evacuation cannot accomplish. D) is wrong because the drier must still be replaced.
A technician performs a triple evacuation on a system that has been open to atmosphere for days. The purpose of breaking the vacuum between pulls is to:
Answer: C — Dilute remaining moisture and non-condensables with dry nitrogen
C) Correct — introducing dry nitrogen between pulls sweeps and dilutes what remains, so each successive evacuation removes a smaller residual. A) is an incidental benefit, not the reason for the procedure. B) describes a standing vacuum test, which is a separate step. D) invents a mechanism; the oil is not heated by breaking vacuum.
Which practice is NEVER acceptable when pressurizing a refrigeration system?
Answer: D — Using oxygen from a welding cylinder as the pressurizing gas
D) Correct — oxygen in contact with refrigeration oil under pressure can detonate, so it must never be used. A) is the standard accepted method. B) is a recognized technique using a small trace charge before nitrogen is added. C) is exactly the discipline that prevents component rupture during testing.
Why is dry nitrogen flowed through copper tubing during brazing of refrigeration joints?
Answer: D — To displace oxygen and prevent formation of black copper-oxide scale
A) Pressure test is a separate step. D) Correct — flowing nitrogen during brazing keeps oxygen out so copper oxide does not form inside the tubing and later plug metering devices or driers. C) Nitrogen does not noticeably accelerate cooling. B) OSHA has no such universal rule.
OSHA refrigeration safety rules around ammonia (R-717) include:
Answer: A — PSM coverage when system contains over 10,000 lbs of ammonia
A) Correct — 29 CFR 1910.119 Process Safety Management applies at 10,000 lbs of ammonia, requiring process hazard analysis, training, MOC, etc. B) Heavily regulated. C) EPA RMP also applies (Risk Management Program). D) Ammonia is widely used.
Why must compressed oxygen never be used to pressurize a refrigeration system for leak testing?
Answer: B — It can react explosively with refrigerant oil
B) Correct — oxygen in contact with hydrocarbon compressor oil under pressure can detonate, which is why only dry nitrogen through a regulator is used. A) is true of compressed air, whose moisture is a problem, but understates the oxygen hazard. C) is irrelevant next to an explosion risk. D) is false; the danger is not a lack of pressure.
When refrigerant contacts an open flame, it can decompose into:
Answer: B — Phosgene and hydrofluoric acid (toxic)
A) Not water. B) Correct — heat causes refrigerant breakdown into phosgene (highly toxic) + HF acid. Never use torch near refrigerant. C) Not just CO₂. D) Very dangerous.
4 cards from the 17 in this chapter.
What happens when refrigerant contacts skin?
Frostbite — refrigerant rapidly evaporates and absorbs heat. Flush with warm water, seek medical care.
What two devices must always be used when pressurizing a system with dry nitrogen?
A pressure regulator on the nitrogen cylinder and a properly sized pressure-relief device on the outlet, so the appliance can never be exposed to the cylinder's full pressure of about 2,000 psig or more.
Why must refrigerant never be pressure-tested or leak-checked with oxygen or compressed air?
Oxygen reacts violently with refrigerant oil and can cause an explosion, and compressed air introduces moisture and can form an ignitable mixture with some refrigerants. Use dry nitrogen with a regulator instead.
What happens when refrigerant contacts an open flame?
Decomposes into toxic phosgene + hydrofluoric acid. Never use torch near refrigerant.
These are a sample. The full Core — Safety, Leak Detection and Evacuation chapter runs 52 items with per-chapter progress tracking, on the web and in the iOS app.
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