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35 multiple-choice questions and 9 flashcards on Type III — Low-Pressure Systems, about 12% of the HVAC: EPA 608 Tech Cert bank. Every one carries a written rationale.
Type III — Low-Pressure Systems 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.
A technician plans a nitrogen pressurization for leak testing on a low-pressure machine. Which control is essential?
Answer: B — A pressure regulator with a relief valve on the nitrogen supply
B) Correct — a regulator with relief protection prevents full cylinder pressure from reaching a vessel with a very low relief setting. A) defeats the protection that keeps the vessel intact. C) raises pressure uncontrollably and removes the water-side heat that protects the tubes. D) misuses a purge unit, which is not a pressurization device.
A technician must pressurize a low-pressure chiller for leak testing. The absolute limit on pressurization is set by:
Answer: A — The rupture disc pressure rating on the machine
A) Correct — a low-pressure machine has a rupture disc that relieves at a low pressure, and exceeding it releases the charge and can damage the machine. B) governs how the recovered refrigerant is stored, not how the machine is tested. C) is a tool capability, not a machine limit, and regulators can far exceed a safe test pressure. D) belongs to the water side and has no bearing on the refrigerant vessel.
R-123 production for servicing existing US chillers is being phased down because:
Answer: B — It is an HCFC under the Montreal Protocol HCFC schedule (production for service ends 2030)
A) B1 class — toxicity managed by ASHRAE 15 ventilation. B) Correct — HCFC schedule allows R-123 service-use production through 2030; new equipment ban earlier. C) Non-flammable. D) Not an HFC.
Why is air entering a low-pressure machine more damaging than a comparable refrigerant leak outward on a high-pressure system?
Answer: C — Air brings moisture that combines with refrigerant to form acid
C) Correct — inbound air carries water vapor, and moisture with refrigerant and heat produces acids that attack tubes, motor insulation and bearings. A) reverses the effect; non-condensables raise condensing pressure and cut capacity. B) misattributes flammability to a nonflammable low-pressure refrigerant. D) describes an oil migration problem unrelated to air ingress.
Before opening a low-pressure chiller to atmosphere for service, the technician must FIRST:
Answer: B — Recover refrigerant to the required vacuum level, isolate the system, and break vacuum with nitrogen — never with air
A) Illegal. B) Correct — break vacuum with dry nitrogen to prevent moisture and air infiltration; opening to air introduces moisture and contributes to acid formation. C) Wrong refrigerant. D) Opening under vacuum draws in air.
What does the rupture disc on a low-pressure chiller protect against?
Answer: D — Overpressure of the machine's shell beyond its design limit
D) Correct — the disc is a pressure relief device for a vessel designed for very low working pressure. A) is handled by flow switches and freeze protection. B) is a control and vane-position issue, not a pressure relief function. C) is protected by oil pressure safeties, a separate circuit.
Which statement about recovery equipment for low-pressure appliances is accurate?
Answer: D — Equipment intended for low-pressure appliances is designed for that duty
D) Correct — low-pressure recovery uses equipment built for large volumes at low pressure, often with high-volume vapor handling. A) ignores the very different volume and pressure conditions. B) is the venting misconception applied to a chiller. C) transplants a Type I passive technique onto equipment where it cannot work.
Centrifugal chillers using low-pressure refrigerant are characterized by:
Answer: A — High volumetric flow of vapor at a low pressure rise
A) Correct — low-pressure refrigerant has a large specific volume, so centrifugal machines move very large vapor volumes at modest pressure rise. B) describes reciprocating machines, a different compression principle. C) is far off; these machines hold hundreds or thousands of pounds. D) reverses the pressure comparison entirely.
ASHRAE Standard 15 requires machinery rooms with low-pressure chillers to have:
Answer: A — Refrigerant sensors and mechanical ventilation to alarm on releases and protect occupants
A) Correct — ASHRAE 15 mandates sensors, ventilation, and emergency procedures sized to refrigerant quantity and toxicity class. B/C/D) Insufficient.
EPA-required final recovery vacuum on a low-pressure appliance manufactured after Nov 15, 1993 is:
Answer: B — 25 mm Hg absolute (~29 in Hg vacuum)
A) Insufficient. B) Correct — low-pressure (e.g., R-123) requires 25 mm Hg absolute final recovery vacuum. C/D) Apply to small or smaller high-pressure appliances. (Recovery to 25 mm Hg absolute is the key Type III value.)
4 cards from the 9 in this chapter.
What does a purge unit do on a low-pressure chiller, and what does a high purge rate indicate?
It removes air and other non-condensables that leak into the machine because the low side runs in a vacuum. A rising purge run time or purge rate is the earliest indication that the machine has developed a leak.
What defines a low-pressure refrigerant, and name two examples.
One with a boiling point above about 10 degrees C that operates in a vacuum on the low side at normal temperatures. Examples: R-11, R-123 and R-113.
What is the maximum pressure that may be used to pressurize a low-pressure appliance for leak testing?
10 psig. Higher pressure risks rupturing the low-pressure shell, whose relief (rupture) disc is typically set at 15 psig.
Type III covers?
LOW-pressure systems: large chillers operating below atmospheric pressure.
These are a sample. The full Type III — Low-Pressure Systems chapter runs 44 items with per-chapter progress tracking, on the web and in the iOS app.
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