HVAC Air Conditioning 4 — Questions and Answers
Question 1: A technician finds that a TXV (thermostatic expansion valve) bulb has lost its charge. What symptom would this most likely cause?
- High suction pressure and flooding of compressor
- Low suction pressure and starved evaporator (Correct answer)
- High discharge pressure and high subcooling
- Compressor short-cycling on high pressure
Correct answer: Low suction pressure and starved evaporator
A TXV with a lost bulb charge will default to a closed or very restricted position, starving the evaporator and resulting in low suction pressure and low superheat at the bulb location.
Question 2: What is the purpose of the reversing valve in a heat pump system?
- Regulate refrigerant flow during defrost
- Reverse the direction of refrigerant flow to switch between heating and cooling modes (Correct answer)
- Control compressor speed during mode changes
- Bypass the metering device in heating mode
Correct answer: Reverse the direction of refrigerant flow to switch between heating and cooling modes
The reversing (four-way) valve switches refrigerant flow direction so the outdoor coil can act as an evaporator in cooling mode and a condenser in heating mode.
Question 3: Which term describes the process of refrigerant absorbing heat and changing from liquid to vapor in the evaporator?
- Condensation
- Sublimation
- Evaporation (vaporization) (Correct answer)
- Compression
Correct answer: Evaporation (vaporization)
Evaporation (or vaporization) is the process by which liquid refrigerant absorbs latent heat from the surroundings and changes to a vapor inside the evaporator coil.
Question 4: What SEER rating is required for new central air conditioners sold in the southeastern United States as of 2023?
- 13 SEER
- 14 SEER
- 15 SEER (SEER2) (Correct answer)
- 16 SEER
Correct answer: 15 SEER (SEER2)
As of January 1, 2023, new AC systems sold in the Southeast and Southwest U.S. must meet a minimum of 15 SEER (or the updated SEER2 equivalent).
Question 5: A capacitor in an air conditioning system serves what primary purpose?
- Store energy for emergency compressor shutdown
- Provide starting torque and improve running efficiency of motors (Correct answer)
- Filter electrical noise from the control board
- Step up voltage to the compressor motor
Correct answer: Provide starting torque and improve running efficiency of motors
Capacitors store electrical charge to provide the phase shift needed for starting single-phase motors (start capacitors) and to improve running efficiency (run capacitors).
Question 6: What does 'latent heat' refer to in HVAC applications?
- Heat transferred by direct contact between surfaces
- Heat that changes the temperature of a substance
- Heat absorbed or released during a phase change without a temperature change (Correct answer)
- Radiant heat from the sun entering through windows
Correct answer: Heat absorbed or released during a phase change without a temperature change
Latent heat is the heat energy absorbed or released when a substance changes phase (e.g., liquid to vapor) without any change in temperature.
Question 7: When recovering refrigerant from a system, the technician must use EPA-approved recovery equipment if the system contains more than how much refrigerant?
- 5 pounds
- 50 pounds
- More than 200 pounds
- Any amount — recovery equipment is always required (Correct answer)
Correct answer: Any amount — recovery equipment is always required
Under EPA Section 608, certified technicians must use approved recovery equipment when servicing any appliance that uses a regulated refrigerant, regardless of charge size.
HVAC Air Conditioning 4
A technician finds that a TXV (thermostatic expansion valve) bulb has lost its charge.
What symptom would this most likely cause?