Chapter 19 Quiz: Air Conditioning and Cooling Systems

Part A: Multiple Choice

1. In the refrigeration cycle, the evaporator coil performs which function?

A) Compresses refrigerant vapor to raise its temperature for heat rejection B) Allows cold, low-pressure refrigerant to absorb heat from house air, cooling the air in the process C) Condenses refrigerant vapor to a liquid by releasing heat to the outdoor air D) Expands high-pressure liquid refrigerant to prepare it for the compressor

2. Your AC system's outdoor unit is blowing warm air. This is:

A) A malfunction — the outdoor unit should always blow cool air B) Normal — the outdoor unit rejects heat extracted from your house into the outdoor air C) A sign that the refrigerant charge is too high D) Normal only during a defrost cycle; otherwise it indicates a problem

3. A homeowner has a 3-ton (36,000 BTU/hr) system with SEER 10. A neighbor has the same size system with SEER 15. If both run 1,000 hours per cooling season, approximately how much more electricity does the SEER 10 system use?

A) About 600 kWh more B) About 1,200 kWh more C) About 2,400 kWh more D) They use the same amount — SEER measures cooling output, not electricity use

4. R-22 refrigerant is no longer manufactured in the United States primarily because:

A) It was found to cause fires in residential settings under certain conditions B) It is a hydrochlorofluorocarbon that depletes the stratospheric ozone layer C) It was less efficient than R-410A at residential operating pressures D) It was incompatible with modern variable-speed compressor technology

5. If you have a central AC system that uses R-22 and it develops a refrigerant leak today, which statement is most accurate?

A) The system can be converted to R-410A by flushing and recharging with the new refrigerant B) Recycled R-22 is available but expensive; repair decisions must weigh cost against system age C) R-22 is completely unavailable and the system cannot be repaired D) The EPA will require you to replace the system within 60 days under current regulations

6. Ice forming on the evaporator coil of a running AC system is typically caused by:

A) The refrigerant charge being too high, causing excessive cooling B) Reduced airflow over the coil (dirty filter, blocked return) or low refrigerant charge C) Outdoor temperatures being too high for efficient operation D) A normal defrost cycle that should clear within an hour without intervention

7. A mini-split system differs from a central split AC system primarily in that:

A) Mini-splits use a different type of refrigerant than central systems B) Mini-splits use a more efficient compressor technology not available in central systems C) Mini-splits deliver conditioned air directly from a room-mounted air handler without ductwork D) Mini-splits can only be used for cooling, while central systems can also heat

8. The SEER2 standard that replaced SEER in 2023 reflects:

A) A new refrigerant-based efficiency metric that replaced the BTU-based SEER calculation B) Updated test conditions that more closely reflect real-world installation and operating conditions C) A mandatory 15% efficiency improvement requirement for all new equipment D) A European efficiency standard adopted by the U.S. for international compatibility

9. During a condensate drain blockage in a central AC system, the most likely outcome (before overflow damage) in modern systems is:

A) The compressor shuts off due to high pressure and the system switches to fan-only mode B) A safety float switch detects rising water in the drain pan and shuts the system off C) The refrigerant charge is automatically reduced to prevent coil icing D) Nothing — the system continues operating and the pan overflows into the living space

10. Why is a window air conditioning unit's condenser side intentionally tilted slightly toward the outside?

A) To improve airflow over the condenser coil in warm weather B) To drain condensate water to the exterior rather than into the room C) To align the unit with prevailing wind direction for better heat rejection D) To prevent the compressor from being level, which would cause oil pooling

Part B: Short Answer

11. Explain why "your air conditioner moves heat; it doesn't create cold" is a more useful way to think about cooling than "the AC makes the air cold." Use the refrigeration cycle to support your answer.

12. A homeowner has a 2006 central AC system that uses R-22. A technician tells them the system has a small refrigerant leak and they need about 2 pounds of R-22 to recharge it, at $80/pound. The same technician says the leak appears to be at the evaporator coil and would cost $1,200 to repair properly before recharging. Total repair: approximately $1,360. A replacement system is quoted at $5,800. The current system has SEER 10; the replacement would be SEER 15. Their annual cooling cost is $480. What should they do, and why?

13. Describe what is happening inside a mini-split system when it heats a room in winter. What component makes it possible for the same device to both heat and cool?

14. A homeowner returns from vacation to find their central AC running but the supply registers blowing room-temperature (not cold) air. What is your step-by-step diagnostic process?

15. What are the key advantages and limitations of mini-splits compared to central ducted AC systems? Under what circumstances would you recommend a mini-split, and when would you recommend central AC instead?

Answer Key

Part A: 1. B 2. B 3. B — SEER 10: (36,000 × 1,000) ÷ (10 × 1,000) = 3,600 kWh; SEER 15: 2,400 kWh; difference = 1,200 kWh 4. B 5. B 6. B 7. C 8. B 9. B 10. B

Part B — Model Answers:

11. The refrigerant cycle works by allowing the evaporator coil to absorb heat from room air (the refrigerant evaporates, carrying heat away) and then transferring that heat to the outdoor air at the condenser (the refrigerant condenses, releasing heat). The room feels cool because heat has been removed, not because cold has been added. This framing helps homeowners understand why a clean filter (airflow over the evaporator), a clear condenser (airflow at the outdoor unit), and correct refrigerant charge (enough refrigerant to carry heat effectively) all matter — each element is part of the heat-moving chain.

12. This is a borderline case. The repair cost ($1,360) divided by annual operating cost savings from replacement ($480 × (15-10)/15 = $160/year) gives a 8.5-year payback for replacement. However, the system is 20+ years old, R-22 is increasingly scarce and expensive, and a 2006 system has likely well exceeded median lifespan. More importantly, the leak is in the evaporator coil — a component that may leak again elsewhere. If they repair and the system fails in 2 years, they've spent $1,360 for nothing. Recommendation: replace. The existing system's age, the R-22 situation, and the evaporator coil location of the leak all favor replacement over repair.

13. In heating mode, the mini-split runs its refrigerant cycle in reverse compared to cooling mode. The outdoor unit's coil acts as the evaporator — the refrigerant absorbs heat from outdoor air (even cold outdoor air contains heat energy relative to absolute zero). The compressor raises refrigerant pressure and temperature, and the indoor unit's coil acts as the condenser, releasing that heat into the room. The component that makes this possible is the reversing valve — a four-way valve that redirects refrigerant flow so that the roles of the indoor and outdoor coils are swapped between heating and cooling modes.

14. Step 1: Check the air filter — a severely clogged filter can reduce airflow enough to cause the indoor coil to ice over, blocking cooling. Step 2: Go to the indoor air handler/furnace and check for ice on the evaporator coil or suction line. If ice is present, shut the system off and let it thaw. Step 3: Check the outdoor unit — is the fan spinning? Is the compressor running (you should hear a hum)? If the outdoor unit isn't running, check the breaker and disconnect. Step 4: After thawing (if ice was found), replace the filter and restart to confirm operation. Step 5: If the system resumes cooling normally, the dirty filter was the cause. If it re-ices or doesn't cool, the problem may be low refrigerant charge — schedule professional service.

15. Mini-splits excel at: targeted room-level comfort without ductwork, heating and cooling additions or spaces not served by central systems, whole-house applications in homes with no existing ductwork, and high-efficiency operation (individual zone control eliminates central system over-conditioning of unoccupied areas). Limitations include: higher per-zone cost than extending existing central ductwork, visible indoor units that some homeowners dislike, and simpler filtration capability. Recommend mini-splits for: rooms without duct service, additions, homes with hydronic (boiler) heat needing cooling-only solution, and new construction in tight homes where duct losses would undermine efficiency. Recommend central AC for: homes with good existing ductwork, occupants who prioritize whole-house filtered and humidified air, or when a budget-constrained replacement makes a central system more cost-effective per square foot of conditioned space.