HVAC Heat Pump Practice Test 3

Question 1: The defrost thermostat closes when the temperature of outdoor coil drops to …………….

• 32 ⁰F
• 42 ⁰F
• 37 ⁰F
• 57 ⁰F

Question 2: Which of the following is the heat sync for air to air heat pump?

• Outdoor air
• Indoor air
• Water
• Ground

Question 3: What is the minimum SEER Rating of cooling as specified by US department of Energy?

• 10.0
• 1.0
• 5.0
• 8.0

Question 4: Which of the following is the measure of overall heating efficiency of heat pump?

• SEER
• HSPF
• COP
• EER

Question 5: Which of the following compressors are mostly used in residential and light commercial constructions?

• Semi hermetic compressors
• Hermetic compressors
• Open type compressors

Question 6: Which of the following is the state of refrigerant at outlet of indoor coil during cooling cycle?

• Liquid
• Gas

Question 7: Which of the following component of heat pump allows the heat pump to operate either in cooling and heating mode?

• Reversing valve
• Expansion valve
• Safety valve
• Pressure relief valve

Question 8: What may be the possible cause for an insufficient heating or cooling in a heat pump?

• Blower not operating
• Incorrect setting of thermostat
• Low refrigerant charge
• High compressor discharge pressure

Question 9: The refrigerant circuit evacuation is said to be complete, when the vacuum pressure reaches ……….. microns or less?

• 500
• 600
• 800
• 1000

Question 10: Which of the following motors require less starting current?

• Single phase
• Poly phase

Question 11: What is a desuperheater in a heat pump system and what is its primary benefit?

• A desuperheater supercharges refrigerant entering the compressor to increase system capacity
• A desuperheater extracts waste heat from the discharge gas to preheat domestic hot water, reducing water heating costs by up to 50% during cooling season
• A desuperheater measures the degree of superheat at the suction line to adjust metering device position
• A desuperheater is a secondary condenser that operates during peak outdoor temperature days

Question 12: What happens to refrigerant during a long off-cycle and what device prevents the associated compressor damage on startup?

• Refrigerant migration is beneficial because it pre-lubricates the compressor before startup
• During the off-cycle refrigerant dissolves into the compressor oil; the crankcase heater prevents this by keeping the compressor warm, avoiding oil foaming and liquid slugging on startup
• A filter drier is the device that prevents refrigerant migration during the off-cycle
• Refrigerant migration only occurs in R-22 systems — modern R-410A systems are not affected

Question 13: What are the advantages of a two-stage (dual-capacity) compressor in a residential heat pump compared to a single-stage compressor?

• A two-stage compressor uses two separate refrigerant circuits to provide twice the cooling capacity
• A two-stage compressor runs at ~65% capacity most of the time for better humidity control, quieter operation, and even temperatures, using 100% only on demand peaks
• Two-stage compressors are less efficient than single-stage because they require more mechanical components
• Two-stage compressors only operate in cooling mode — they cannot use two stages in heating mode

Question 14: What is a variable speed (inverter-driven) heat pump compressor and how does it differ from single-stage and two-stage compressors?

• Variable speed compressors run at two fixed speeds controlled by outdoor temperature sensors
• Variable speed (inverter) compressors continuously modulate between ~20-120% capacity to precisely match building load, achieving the highest efficiency and comfort of any compressor type
• Variable speed compressors are only used in commercial systems because they require three-phase power
• Variable speed compressors eliminate the need for a reversing valve in heat pump applications

Question 15: What is the minimum outdoor temperature for heat pump cooling operation and why?

• Heat pumps can cool down to -40°F outdoor temperature without any special equipment
• Standard heat pumps cannot cool effectively below ~55-65°F outdoor temperature because condensing pressure drops too low; low ambient kits or variable speed compressors are needed for lower temperatures
• The minimum outdoor temperature for cooling is 32°F — the heat pump cannot operate at sub-freezing temperatures
• Low outdoor temperature actually improves heat pump cooling efficiency — the colder the outdoor air the better

Question 16: What is duct blaster testing and why is duct leakage a significant concern in heat pump systems?

• Duct leakage is not a concern because leaked conditioned air stays within the building
• A duct blaster measures duct leakage by pressurizing the system; leaky ducts in unconditioned spaces directly waste conditioned air, reducing heat pump efficiency and increasing costs
• Duct blaster testing is only required for commercial HVAC systems over 5 tons
• Duct leakage actually helps the heat pump cool the attic and reduce roof damage

Question 17: Why do most heat pump systems use a Thermostatic Expansion Valve (TXV) rather than a fixed orifice or capillary tube as the metering device?

• TXVs are used because they are less expensive than fixed orifice metering devices
• TXVs automatically maintain constant superheat across wide operating temperature ranges, essential for heat pumps that must perform efficiently from very cold to very hot outdoor conditions
• Fixed orifice devices cannot be used with R-410A refrigerant due to incompatibility
• TXVs are required only in systems over 5 tons — residential heat pumps can use fixed orifice devices

Question 18: At what outdoor temperature does a heat pump's COP fall to 1.0, meaning it delivers no more heat than electric resistance heating?

• A heat pump's COP never reaches 1.0 — it always outperforms electric resistance heating
• The COP crossover occurs at approximately 17-25°F for standard heat pumps — below this the heat pump provides no efficiency advantage over resistance strips
• A heat pump COP reaches 1.0 at 45°F — above this it is less efficient than resistance heating
• COP crossover only applies to cooling mode — in heating mode COP remains constant regardless of outdoor temperature

Question 19: A heat pump outdoor unit trips the high pressure cutout in cooling mode. The condenser fan is NOT running. What is the likely cause and diagnostic sequence?

• A stopped condenser fan is normal in certain outdoor temperature conditions — reset the high pressure switch and continue operation
• A stopped condenser fan prevents heat rejection from the outdoor coil in cooling mode, causing rapid pressure rise and high pressure cutout; check capacitor (most common), motor windings, and voltage in that order
• The high pressure cutout tripped due to refrigerant overcharge — add more refrigerant to bring pressure down
• A stopped condenser fan only affects heating mode — it is not related to high pressure in cooling

Question 20: What determines the maximum length of refrigerant line sets in a split heat pump system, and what problems occur with lines that are too long?

• Refrigerant lines can be any length without affecting performance — only the refrigerant charge amount matters
• Line length is limited by pressure drop, oil return requirements, and manufacturer specifications; excessive length causes capacity reduction, oil starvation, and flash gas before the metering device
• Longer refrigerant lines are preferred because they provide more subcooling before the metering device
• Only the suction line length matters — liquid line length has no effect on system performance

Question 21: A heat pump that has been neglected for three years without maintenance shows high head pressure, high discharge temperature, and excessive compressor amperage. What maintenance item most likely explains these symptoms?

• The symptoms indicate refrigerant overcharge — remove refrigerant to reduce head pressure
• A dirty outdoor coil most likely causes these symptoms by restricting airflow and reducing heat rejection; coil cleaning restores normal pressures, temperatures, and amperage
• High head pressure, discharge temperature, and amperage indicate a faulty high-pressure switch — replace it
• These symptoms only occur in the first year of operation and resolve on their own as the system breaks in

Question 22: What is the function of the outdoor thermostat (OAT sensor) in a heat pump control system?

• The OAT sensor measures outdoor humidity to determine when dehumidification is needed
• The OAT sensor controls auxiliary heat staging, compressor lockout, and defrost permissions based on outdoor temperature to optimize efficiency
• The OAT sensor is only used for display purposes — it has no control function in the heat pump system
• The OAT sensor controls the reversing valve direction based on outdoor temperature

Question 23: A technician needs to replace the reversing valve on a heat pump. What is required before the valve can be replaced?