SkyDrill

Compressor oil quantity per pound of refrigerant

Aviation Mechanic Airframe (AMA) practice question 9 of 15 on Environmental Systems. ACS element AM.II.G.R4 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA vapor cycle system is charged with 4 pounds of refrigerant and the standard ratio of oil to refrigerant is used. Approximately how much oil goes into the system?

  1. AAbout 4 ounces
  2. BAbout 16 ounces
  3. CAbout 1 ounce
Show the answer and explanation

Correct answer: C. About 1 ounce

  • A — incorrect This assumes one ounce per pound, four times the standard quarter-ounce ratio.
  • B — incorrect A full pint of oil in a 4-pound charge is far beyond the standard ratio and is not supported by the servicing guidance.
  • C — correct The standard amount is approximately one-quarter ounce of oil for each pound of refrigerant, so 4 pounds calls for about 1 ounce.

BACKGROUND

The compressor in a vapor cycle system is a sealed unit lubricated with oil, and any time the system is purged is an opportunity to check the oil quantity in the compressor crankcase. Oil quantity added to the system is specified by the manufacturer, and approximately one-quarter ounce of oil for each pound of refrigerant is a standard amount. Refrigerant premixed with oil is available and may be permissible for use, which eliminates the need to add oil separately. On a servicing cart, the amount of oil to put into the system can be selected on the unit. In every case the manufacturer's specifications govern, including the total refrigerant charge, which is measured in pounds.

STUDY TIP

Use the quarter-ounce-per-pound figure only as the general standard and verify it against the aircraft's service data on the job. Exam calculations of this kind usually just need the ratio applied to a stated charge weight.

KEY POINTS

  • Standard oil is about one-quarter ounce for each pound of refrigerant.
  • Manufacturer specifications always govern the actual oil and refrigerant quantities.
  • Premixed refrigerant and oil may be permissible, removing the separate oil step.

SOURCES

  • sources/ama-airframe/ch16.txt "Charging the System"
  • sources/ama-airframe/ch16.txt "Visual Inspection"
  • sources/ama-airframe/ch16.txt "Refrigerant Source"
Practice the Aviation Mechanic Airframe (AMA) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON ENVIRONMENTAL SYSTEMS

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.