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NATE Exam: Air Conditioning and Heat
Pumps
The maximum sensible cooling capacity of a heat pump should be within ____% of the calculated sensible heat gain of a structure with a large heating load. a. ±10% b. +15% c. - 25% d. +25% - CORRECT ANSWER-d (+25%) The combined output of a heat pump and its auxiliary heat should not exceed the calculated heat loss of a home by more than ____%. a. 10% b. 15% c. 20% d. 25% - CORRECT ANSWER-b (15%) What amount of auxiliary electric heat is needed when the output of a heat pump on a design day equals 18,800 Btuh and the heat loss of a home is 29,700 Btuh? a. 2.1 kWh b. 3.2 kWh c. 5.0 kWh d. 10.9 kWh Note: 3,413 Btu/kW - CORRECT ANSWER-b (3.2 kWh) The three processes that transfer heat energy are conduction, convection, and ____. a. concentration b. radiation c. refraction d. static pressure - CORRECT ANSWER-b (radiation) Heat transfer that occurs when substances of different temperatures are in contact with each other is called ____. a. concentration b. conduction c. convection
d. radiation - CORRECT ANSWER-b (conduction) What effect does raising the pressure in a sealed system have on refrigerant? a. It becomes more difficult to subcool the liquid refrigerant b. It becomes more difficult to superheat the refrigerant vapor c. The refrigerant's boiling point decreases d. The refrigerant's boiling point increases - CORRECT ANSWER-d (The refrigerant's boiling point increases) Which of the following factors affects a customer's level of comfort? a. Air movement b. Humidity c. Temperature d. All of the above - CORRECT ANSWER-d (All of the above: air movement, humidity, temperature) A cooling load calculation estimates the sensible heat gain of a structure. The maximum sensible capacity of a cooling-only system should be within ____% of this calculated value. a. ±10% b. +10% c. +15% d. +30% - CORRECT ANSWER-c (+15%) What is the primary danger to people near an accidental refrigerant release or spill? a. Blurred vision caused by the refrigerant vapor coming in contact with the eyes b. Changes in weather patterns caused by global warming c. Damage to the food chain caused by decreased ozone levels in the stratosphere d. Suffocation caused by the heavier refrigerant displacing oxygen in the air - CORRECT ANSWER-d (Suffocation caused by the heavier refrigerant displacing oxygen in the air) The maximum temperature at which refrigerant may be stored is ____°F when the container is no more than ____% full of liquid by volume. a. 120°F, 60% b. 125°F, 60% c. 125°F, 80% d. 135°F, 80% - CORRECT ANSWER-c (125°F, 80%) Boiling of the refrigerant occurs in which system component?
c. Condenser d. Evaporator - CORRECT ANSWER-b (Compressor) How are hermetic compressor motors cooled? a. With air drawn around the compressor shell by the condenser fan b. With water circulated through tubing wrapped around the compressor shell c. With suction vapor drawn from the evaporator d. With a combination of air and water - CORRECT ANSWER-c (With suction vapor drawn from the evaporator) Heat pump compressors sometimes run hotter than compressors used in cooling-only units because heat pump compressors ____. a. exhibit low refrigerant density at low suction pressures during the heating cycle b. pump liquid refrigerant during the cooling cycle c. must prevent ice formation during the defrost cycle d. must heat indoor spaces in the winter - CORRECT ANSWER-a (exhibit low refrigerant density at low suction) When is a crankcase heater most needed? a. Early in the morning during the cooling cycle b. When the compressor is operating in very cold winter weather c. When the compressor is operating in very humid conditions d. When the compressor is off - CORRECT ANSWER-d (When the compressor is off) Work done on the refrigerant in the condenser is transferred as ____. a. latent heat b. sensible heat c. specific heat d. both sensible and latent heat - CORRECT ANSWER-d (both sensible and latent heat) Why are more circuits needed in the outdoor coils used in heat pumps than in the condenser coils used in cooling-only units? a. To keep the pressure drop across the outdoor coil high b. To keep the pressure drop across the outdoor coil low c. To provide more subcooling during the cooling cycle d. To provide more subcooling during the heating cycle - CORRECT ANSWER-b (To keep the pressure drop across the outdoor coil low) What is the typical water flow rate per ton of cooling for water-source heat pumps operating in closed-loop systems?
a. 3.0 gpm per ton b. 2.5 gpm per ton c. 2.0 gpm per ton d. 1.5 gpm per ton - CORRECT ANSWER-a (3.0 gpm per ton) What tool should be used to shorten a capillary tube? a. A pair of pliers with side-cutter edges b. A small tubing cutter c. Any tubing cutter approved for use on refrigerant tubing d. A triangular or knife-edge file - CORRECT ANSWER-d (A triangular or knife-edge file) Which pressure in a TEV is the opening pressure? a. Bulb pressure b. Evaporator pressure c. Spring pressure d. A combination of bulb and spring pressures - CORRECT ANSWER-a (Bulb pressure) What affect does a low refrigerant charge have on reversing valve operation? a. It causes the slider to overheat b. It creates a hissing sound in the reversing valve c. It increases the chance that the reversing valve will not be able to transfer properly d. It has no effect on reversing valve operation - CORRECT ANSWER-c (It increases the chance that the reversing valve will not be able to transfer properly) When adding a heat pump to an existing fossil-fuel furnace, an installer must do all of the following except ____. a. add a control to prevent the heat pump and furnace from operating at the same time during normal heating b. confirm there is adequate clearance around the outdoor section for good air flow c. level the indoor coil's condensate pan to ensure proper drainage of condensate water d. make sure that the number of fins per inch of the new coils equals that of the replaced coils - CORRECT ANSWER-d (make sure that the number of fins per inch of the new coils equals that of the replaced coils) What is the purpose of a receiver? a. It prevents liquid refrigerant from slugging the compressor b. It removes heat from refrigerant vapor c. It returns oil to the compressor at a rate the compressor can tolerate d. It stores liquid refrigerant - CORRECT ANSWER-d (It stores liquid refrigerant)
Voltage supplied to a motor may vary from the rated voltage by ____%. a. +0%, - 0% b. +0%, - 10% c. +10%, - 0% d. +10%, - 10% - CORRECT ANSWER-d (+10%, - 10%) What is one of the most important reasons for using electronic controls in HVACR systems? a. The Clean Air Act of 1990 mandates their use b. They are less expensive than the controls they replace c. They are lighter in weight than the controls they replace d. They make decisions based on many inputs - CORRECT ANSWER-d (They make decisions based on many inputs) Hard-start kits are often needed on ____. a. reciprocating compressors used with TEVs b. rotary compressors used with fixed metering devices c. scroll compressors used with TEVs d. three-phase compressor used with fixed metering devices - CORRECT ANSWER-a (reciprocating compressors used with TEVs) A 24-V transformer with a 40-VA rating can operate safely with a current of ____. a. 6.0 mA b. 960.0 mA c. 0.6 A d. 1.67 A - CORRECT ANSWER-d (1.67 A) Some electromechanical thermostats must be connected to both sides of the transformer in order to power the ____. a. cooling anticipator b. display lights on the subbase c. heat anticipator d. microprocessor - CORRECT ANSWER-b (display lights on the subbase) A cooling anticipator in the control circuit is connected in ____ with the ____ switch of the thermostat. a. parallel, cooling b. parallel, heating c. series, cooling
d. series, heating - CORRECT ANSWER-a (parallel, cooling) According to Ohm's Law, what will happen if voltage to a heater element is increased by 10%? a. The Btuh output will increase by 5% b. The current draw will decrease by 10% c. The current draw will increase by 10% d. The heater will overheat - CORRECT ANSWER-c (the current draw will increase by 10%) When air flow through an electric heater is not sufficient, the technician will observe ____. a. fusible links glowing red or orange b. heater elements glowing red or orange c. higher-than-normal voltage readings d. lower-than-normal voltage readings See page 78 - CORRECT ANSWER-b (heater elements glowing red or orange) Which of the following combination of measurements indicates an open heater element? a. Current draw through the heater elements with no voltage to the heater b. Voltage to the heater with current draw through the heater elements c. Voltage to the heater with no current draw through the heater elements d. voltage to the heater with resistance measured by an ohmmeter - CORRECT ANSWER-c (Voltage to the heater with no current draw through the heater elements) Which of the following functions occur when a heat pump goes into a defrost cycle? a. The auxiliary heat comes on, the outdoor fan stops running, and the reversing valve switches to the cooling mode b. The outdoor fan stops running and the reversing valve switches to the cooling mode c. The reversing valve switches to the cooling mode and the auxiliary heat comes on d. The reversing valve switches to the heating mode, the outdoor fan stops running, and the auxiliary heat comes on - CORRECT ANSWER-a (The auxiliary heat comes on, the outdoor fan stops running, and the reversing valve switches to the cooling mode) What internal voltage is likely to be measured in an electronic air cleaner? a. 24 V b. 120 V c. 380 V d. 5,000 V
Which of the following statements about a packaged unit installation is true? a. Packaged heat pumps are intended for rooftop installations only b. Packaged heat pumps are more difficult to install than split systems c. Packaged heat pumps are not available for use in commercial applications d. The pad used to support a packaged heat pump should not make contact with the building - CORRECT ANSWER-d (The pad used to support a packaged heat pump should not make contact with the building) Which of the following brazing materials is acceptable for use on refrigerant piping? a. 50/50 soft solder with an approved flux b. 95/5 soft solder with an approved liquid flux c. 95/5 soft solder with an approved paste flux d. Brazing allow with an approved flux See pages 97, 101 - CORRECT ANSWER-d (Brazing allow with an approved flux) What type of flame is recommended for brazing refrigerant piping? a. Acetylene flame b. Carbonizing flame c. Neutral flame d. Oxidizing flame See page 100 - CORRECT ANSWER-c (Neutral flame) Why must you exercise special care when you bend soft-drawn refrigerant tubing? a. Any distortion of the tubing diameter creates a restriction to refrigerant flow that reduces system capacity b. Copper flakes can come loose from interior surfaces of the tubing if it is overbent c. Overbending the tubing makes it difficult to slide on the close-cell insulation d. The refrigeration flow rate increases if tubing is overbent, making oil return impossible
- CORRECT ANSWER-a (Any distortion of the tubing diameter creates a restriction to refrigerant flow that reduces system capacity) The evacuation of a refrigerant circuit is considered complete when a vacuum of ____ can be maintained. a. 200 microns b. 350 microns c. 500 microns d. 1,000 microns - CORRECT ANSWER-c (500 microns)
As the length of electrical wire increases, its resistance ____ while the temperature is maintained at a constant level. a. decreases b. increases d. remains unchanged c. varies unpredictably - CORRECT ANSWER-b (increases) What is the thermal balance point of a heat pump system? a. The indoor air temperature at which the blower fan speed must be increased in order to maintain the space temperature setpoint b. The outdoor air temperature at which the heat pump initiates a defrost cycle c. The outdoor air temperature at which output of the gas furnace in a dual-fuel application equals the heat loss of the home d. The outdoor air temperature at which the output of the heat pump equals the heat loss of the home - CORRECT ANSWER-d (The outdoor air temperature at which the output of the heat pump equals the heat loss of the home) What voltage is measured between any two legs of the three hot legs in a delta- connected 240-V three-phase distribution panel? a. 208 V b. 240 V c. 277 V d. 380 V See page 107 - CORRECT ANSWER-b (240 V) Which of the following statements about the installation of an electric air cleaner (EAC) is true? a. An EAC should be wired so that it operates only when the ON/OFF switch is in the "ON" position and the supply air blower is operating b. The control voltage supplied to an EAC can be as high as 5,000 V c. The primary function of an EAC is odor removal d. When the relative humidity is low, an EAC should be operated only in the heating mode - CORRECT ANSWER-a (An EAC should be wired so that it operates only when the ON/OFF switch is in the "ON" position and the supply air blower is operating) What is the indoor air flow for an electric furnace when the supply air temperature is 98°F, the return air temperature is 70°F, the voltage supplied to the furnace is 220 V, and the current draw of the furnace is 47 A? a. 1,060 CFM b. 1,170 CFM
d. shielded cable - CORRECT ANSWER-b (field-installed wiring) All safety switches must be ____. a. connected in parallel with the control switch b. connected in series with the control switch c. normally closed limit switches d. open at the same time in order to protect the load - CORRECT ANSWER-b (connected in series with the control switch) Which of the following statements about SI wiring diagrams is true? a. High-voltage wiring circuits are shown above the power wiring b. High voltage wiring circuits are shown below the power wiring c. Low-voltage wiring circuits are shown below the power wiring d. Power wires are drawn as perimeter lines with circuits drawn between the power wires - CORRECT ANSWER-b (High-voltage wiring circuits are shown below the power wiring) Which of the following types of wiring diagrams is best suited for troubleshooting electric circuits? a. Installation diagram b. Ladder schematic c. Pictorial diagram d. Point-to-point diagram - CORRECT ANSWER-b (Ladder schematic) Exposure to an electric current of ____ mA can be fatal if it lasts for one second or more. a. 1 mA b. 10 to 20 mA c. 50 to 75 mA d. 100 to 200 mA See pages 145- 146 - CORRECT ANSWER-d (100 to 200 mA) The use of a ground fault circuit interrupter (CFCI) is especially important when ____. a. apprentice workers are asked to use power tools b. more than one electric tool is plugged into an outlet c. the cord of an electric tool is frayed or cracked d. work is being done on wet surfaces - CORRECT ANSWER-d (work is being done on wet surfaces)
An auto-ranging meter automatically finds the best measurement range to display the quantity of ____ being measured. a. amperes or ohms b. amperes or volts c. ohms or volts d. amperes, ohms, volts - CORRECT ANSWER-d (amperes, ohms, volts) What ANSI category is best for meters used in HVACR electrical work, and why? a. CAT I, because most HVACR electrical work is done on control circuits b. CAT II, because most HVACR electrical work is done on appliances that plug into wall receptacles c. CAT III, because most HVACR electrical work is done on appliances that are permanently installed d. CAT IV, because most HVACR electrical work is done on utility connections - CORRECT ANSWER-c (CAT III, because most HVACR electrical work is done on appliances that are permanently installed) What critical first step must be taken to begin the troubleshooting process? a. Check all fuses for continuity b. Check for grounded motor windings c. Check relay and contactor housings for stuck switches d. Check that the correct voltage is being supplied to the equipment - CORRECT ANSWER-d (Check that the correct voltage is being supplied to the equipment) A good fuse will yield a reading of ____ on an ohmmeter. a. 0 Ω b. less than 1 Ω c. infinity d. a value that rises quickly to 0 before falling slowly toward infinity - CORRECT ANSWER-a (0 Ω) Which of the following low-voltage wires is typically used to carry power to the thermostat subbase? a. Green b. Red c. White d. Yellow - CORRECT ANSWER-b (Red) Which terminal designation on the thermostat subbase typically is used for the cooling circuit?
a. Fusible link b. High-limit switch c. Main circuit fuse d. Sequencer See page 159 - CORRECT ANSWER-d (Sequencer) A resistance reading of infinity between the "R" terminal and the "S" terminal of a compressor motor indicates a(n) ____. a. grounded motor winding b. open motor winding c. shorted motor winding d. tripped internal overload - CORRECT ANSWER-b (open motor winding) An acceptable capacitance reading for a run capacitor is ____ the microfarad rating printed on the capacitor. a. equal to or up to 10% more than b. equal to or up to 20% more than c. plus or minus 10% of d. plus or minus 20% of - CORRECT ANSWER-c (plus or minus 10% of) What air volume flow rate of recirculated indoor air equals one ton of cooling load on the evaporator? a. 300 cfm b. 350 cfm c. 400 cfm d. 450 cfm - CORRECT ANSWER-c (400 cfm) What heat quantity equals one ton of total cooling load on the evaporator? a. 7,500 Btuh b. 10,000 Btuh c. 12,000 Btuh d. 15,000 Btuh - CORRECT ANSWER-c (12,000 Btuh) Which of the following is measured to determine the total resistance to air flow in a ductwork system? a. Current draw of the compressor motor b. External static pressure at the air handler or furnace c. Power input to the electric heater d. Temperature rise across the electric heater - CORRECT ANSWER-b (External static pressure at the air handler or furnace)
External static pressure is the sum of the ____ and the ____. a. absolute static pressure entering the air filter, absolute static pressure leaving the air filter b. absolute static pressure entering the indoor blower, absolute static pressure leaving the indoor blower c. absolute supply static pressure, absolute return static pressure d. static pressure entering the evaporator coil, static pressure leaving the evaporator coil See page 172 - CORRECT ANSWER-c (absolute supply static pressure, absolute return static pressure) What is the output of a residential electric furnace when the voltage impressed is equal to 235 V and its current draw is 40 A? a. 10,150 Btuh b. 29,530 Btuh c. 32,080 Btuh d. 42,300 Btuh Btuh = W x 3. W = V x A See page 175 - CORRECT ANSWER-c (32,080 Btuh) Use the collected service data below to calculate the air flow volume for a residential electric furnace: Voltage = 240 V ac Current draw = 40 A Entering air temperature = 70°F Leaving air temperature = 105°F a. 798 cfm b. 867 cfm c, 936 cfm d. 1,100 cfm cfm = (voltage x current x 3.413) / (temperature rise x 1.08) - CORRECT ANSWER-b (867 cfm) What is the maximum recommended face velocity for air leaving a supply register? a. 300 ft/min b. 450 ft/min c. 500 ft/min
What gas must be purged through a refrigerant circuit to prevent the formation of oxides whenever brazing is being done? a. Any HFC b. Dry nitrogen c. Filtered air d. Oxygen - CORRECT ANSWER-b (Dry nitrogen) What certification is required before a technician is permitted to work on air conditioning and heat pump systems? a. ARI 77-88 certification b. EPA Section 608 certification c. EPA Section 609 certification d. Journey or Master Mechanical tradesman license - CORRECT ANSWER-b (EPA Section 608 certification)
