NATE Heat Pumps 1 — Questions and Answers
Question 1: What component allows a heat pump to reverse the refrigeration cycle between heating and cooling modes?
- Check valve
- Reversing valve (Correct answer)
- Thermostatic expansion valve
- Accumulator
Correct answer: Reversing valve
The reversing valve redirects refrigerant flow so the indoor coil acts as a condenser in heating mode and an evaporator in cooling mode.
Question 2: At what outdoor temperature do most standard air-source heat pumps reach their balance point?
- 50°F
- 40°F
- 35–40°F (Correct answer)
- 25°F
Correct answer: 35–40°F
The balance point is typically 35–40°F, where the heat pump output equals the building heat loss and auxiliary heat is not yet needed.
Question 3: What is the purpose of the accumulator in a heat pump system?
- Store excess refrigerant charge
- Prevent liquid refrigerant from entering the compressor (Correct answer)
- Remove non-condensables from the refrigerant
- Regulate condenser airflow
Correct answer: Prevent liquid refrigerant from entering the compressor
The accumulator is located on the suction line and traps liquid refrigerant, allowing only vapor to reach the compressor.
Question 4: During a heating cycle, which coil in a heat pump acts as the evaporator?
- Indoor coil
- Outdoor coil (Correct answer)
- Auxiliary coil
- Desuperheater coil
Correct answer: Outdoor coil
In heating mode, the outdoor coil absorbs heat from the outside air (acting as evaporator) and the indoor coil releases heat (acting as condenser).
Question 5: What initiates a defrost cycle on an air-source heat pump?
- Indoor thermostat calling for auxiliary heat
- Time/temperature or pressure differential control sensing frost buildup on outdoor coil (Correct answer)
- Outdoor ambient thermostat dropping below 32°F
- Compressor high-pressure lockout
Correct answer: Time/temperature or pressure differential control sensing frost buildup on outdoor coil
Defrost controls typically use a combination of time and outdoor coil temperature (or pressure differential) to trigger defrost when frost accumulates.
Question 6: What does COP (Coefficient of Performance) measure for a heat pump?
- Cooling capacity in BTUs
- Ratio of heat output to electrical energy input (Correct answer)
- Seasonal energy efficiency ratio
- Compressor displacement volume
Correct answer: Ratio of heat output to electrical energy input
COP is the ratio of heat energy delivered to electrical energy consumed; a COP of 3 means 3 units of heat per 1 unit of electricity.
NATE Heat Pumps 1
What component allows a heat pump to reverse the refrigeration cycle between heating and cooling modes?