HVAC Refrigeration 5 — Questions and Answers
Question 1: What is the purpose of pulling a vacuum (evacuating) a refrigeration system before charging?
- Test the compressor capacity before adding refrigerant
- Remove air, nitrogen, and moisture from the system (Correct answer)
- Measure the exact internal volume of the system
- Pre-cool the evaporator before refrigerant is introduced
Correct answer: Remove air, nitrogen, and moisture from the system
Evacuation removes air, non-condensable gases, and moisture from the system to prevent contamination, acid formation, and ice blockages.
Question 2: Which component in a refrigeration system separates refrigerant vapor from liquid to ensure only vapor enters the compressor in a flooded evaporator system?
- Filter-drier
- Suction accumulator (Correct answer)
- Liquid receiver
- Sight glass
Correct answer: Suction accumulator
A suction accumulator is installed in the suction line to separate and hold any liquid refrigerant, allowing only vapor to pass to the compressor.
Question 3: What does a sight glass/moisture indicator show when the refrigerant system is properly charged and dry?
- Bubbles and a yellow indicator dot
- A clear (bubble-free) window with a green indicator dot (Correct answer)
- A frosted glass with no visible flow
- Intermittent flashing between clear and bubbly
Correct answer: A clear (bubble-free) window with a green indicator dot
A properly charged, dry system shows a clear sight glass with no bubbles and a green moisture indicator dot; bubbles indicate low charge and yellow indicates moisture.
Question 4: In a heat pump system, which component reverses the refrigerant flow direction to switch between heating and cooling modes?
- Check valve
- Four-way reversing valve (Correct answer)
- Two-position expansion valve
- Bypass solenoid valve
Correct answer: Four-way reversing valve
A four-way reversing valve redirects refrigerant flow so the outdoor coil becomes the evaporator in cooling mode and the condenser in heating mode.
Question 5: What is the minimum vacuum level (in microns) generally considered acceptable before charging a refrigeration system?
- 5,000 microns
- 2,000 microns
- 500 microns (Correct answer)
- 100 microns
Correct answer: 500 microns
The industry standard is to pull a vacuum to 500 microns or lower before charging, ensuring adequate moisture removal and leak verification.
Question 6: What is the Ozone Depletion Potential (ODP) of R-410A refrigerant?
- 1.0 (same as R-11)
- 0.05
- 0.055 (same as R-22)
- 0 (zero) (Correct answer)
Correct answer: 0 (zero)
R-410A has an ODP of zero because it contains no chlorine atoms that could destroy stratospheric ozone, unlike older refrigerants such as R-22.
Question 7: When adding refrigerant to a system that uses a blended refrigerant (such as R-410A), how must it be charged?
- As a vapor through the high-pressure side only
- As a liquid from the refrigerant cylinder (Correct answer)
- As a vapor through the low-pressure side only
- Either liquid or vapor — blends are not affected by charging method
Correct answer: As a liquid from the refrigerant cylinder
Blended refrigerants like R-410A must be charged as a liquid to prevent fractionation, where different components evaporate at different rates, changing the blend composition.
HVAC Refrigeration 5
What is the purpose of pulling a vacuum (evacuating) a refrigeration system before charging?