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Why refrigerant recovery needs a service unit

Aviation Mechanic Airframe (AMA) practice question 6 of 15 on Environmental Systems. ACS element AM.II.G.R1 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONWhy can a vapor cycle system not be completely emptied of refrigerant by letting it flow into a collection container on the manifold center hose?

  1. AContainer pressure drops below zero psi.
  2. BPressures equalize above atmospheric.
  3. CThe oil separates from refrigerant.
Show the answer and explanation

Correct answer: B. Pressures equalize above atmospheric.

  • A — incorrect No vacuum forms in the container during a simple transfer; the problem is that the two pressures equalize while still above atmospheric.
  • B — correct The system and the container come to equal pressure while still above atmospheric, so part of the charge stays in the system; an independent compressor and collection system is required.
  • C — incorrect Recovery units do recycle oil as well as refrigerant, but oil separation is not what prevents a gravity or pressure transfer from emptying the system.

BACKGROUND

The Environmental Protection Agency has declared it illegal to release R12 refrigerant into the atmosphere, and equipment has been designed to capture refrigerant during servicing. Although R134a is not under the same federal restriction, releasing it is illegal in some locations, and capturing all refrigerants for future use is good practice. Regulations requiring capture have limited the use of the plain manifold set, which can still charge a system but cannot empty one. Allowing refrigerant to flow into a collection container attached to the center hose will not capture the entire charge, because the system and container pressures equalize above atmospheric pressure, so an independent compressor and collection system is required. Modern all-in-one service carts build in the manifold set, a purging compressor, a vacuum pump and recycling filters for refrigerant and oil.

STUDY TIP

Purging a system means emptying it of its charge, and it must be done with a recovery-capable cart before any component is opened. Remember that the EPA also requires certification of technicians who work with vapor cycle refrigerant and equipment.

KEY POINTS

  • A simple transfer leaves refrigerant behind because pressures equalize above atmospheric.
  • Recovery requires a service unit with its own compressor and collection system.
  • Releasing R12 to the atmosphere is illegal, and capturing all refrigerants is good practice.

SOURCES

  • sources/ama-airframe/ch16.txt "Full Service Refrigerant Recovery, Recycling, Evacuation, & Recharging Units"
  • sources/ama-airframe/ch16.txt "Vapor Cycle Air Conditioning Servicing Equipment"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.