HVAC NATE Heat Pump- Exam 2023 Questions and Answers

On an R-22 system, line diameters and lengths are typically specified for a vapor pressure drop that does not exceed what? - ANSWER-6-7PSI or 6F What is the primary purpose of using flux when soldering copper or brass parts? - ANSWER-Prevent Oxidation The water that results from a defrost cycle of an air to air heat pump(runoff) must? - ANSWER-Drain off and away from the outdoor coil. Why must the runoff be drained off and away from the outdoor coil? - ANSWER-Excessive ice can build up on the bottom of the coil and can reduce capacity. What is the component that reduces sound transmission and prevents water leaks of a package heat pump installed on a roof? - ANSWER-Curb Gasket Why do you need to add a control for a heat pump indoor coil that is installed on a fossil fuel furnace? - ANSWER-So the heat pump and furnace do not operate at the same time in normal heating. What happens when you energize a hermetic refrigeration compressor and the system is in a deep vacuum? - ANSWER-Motor windings could become damaged. What needs to happen in order to consider an evacuation to be complete? - ANSWER-System should be evacuated to a vacuum of 500 Microns or below. A system is supplied from the factory with charge for a 15 foot line set. The data plate shows the required system charge to be 5 pounds 10 ounces. The line set uses a 3/8 inch liquid line and is 25 feet long. The manufacturer's instruction sheet specifies 0.6 ounces of refrigerant to be added for each added foot of refrigerant line length. How much refrigerant is needed to completely charge the system? - ANSWER-6lbs Where are drive slips typically installed? - ANSWER-On the shorter sides of rectangular duct. What is a necessary check to properly set a heat anticipator? - ANSWER-Heating control circuit amperage draw. A heat pump operating in normal ice free conditions maintains a certain temperature difference between the outdoor coil temperature and the surrounding outdoor ambient. What is this temperature referred to as? - ANSWER-Coil TD. What is the smallest refrigerant leak that an electronic leak detector should be capable of sensing? - ANSWER-.o5oz per year. When checking the pressures in an operating system with a manifold gauge set, will refrigerant oil in a hose will have an effect on the gauge? - ANSWER-No What is the absolute pressure at sea level if a gauge pressure is 35 psig? - ANSWER-49.7psia 100,000 BTUH output furnace. Return air temp is 65F. Supply air is 135F. What is the CFM? - ANSWER-1323CFM What is the best method of repair when a residential supply diffuser is noisy because of a loose vane? - ANSWER-Replace the diffuser. When performing preventive maintenance on a heat pump what should the technician check and why? - ANSWER-Outdoor fan. To be certain it runs freely with no binding. What is the effect of 170 volts supplied to a 208/230 volt compressor? - ANSWER-Would cause the current to increase and the motor may trip on overload. On a service call for a cooling problem with a heat pump, your inspections find a liquid line that has condensation on it. What is most likely to cause this? - ANSWER-Restriction in the liquid line. What is a reason for cool air complaints when a heat pump is operating in the heating cycle? - ANSWER-Excessive supply air velocities. The following measurements are recorded on an operating heat pump system. The heat pump is operating with the compressor only with no auxiliary heat: • Heat pump only supply air temperature 92°F • Heat pump only return air temperature 70°F • Outdoor temperature 54°F • Supply air temp. /auxiliary heat ON 115°F • Return air temp. /auxiliary heat ON 70°F • CFM 1228 What is the heating capacity in BTUH? - ANSWER-29,177 BTU/H Inadequate heating can be caused by what? - ANSWER-Dirty or clogged air filter. To minimize noise problems in residential duct systems, what is the range (recommended to maximum) of design air velocity in the rectangular main supply trunk? - ANSWER-700 to 900 fpm conditions while checking a packaged heat pump in cooling. • The unit has a piston type metering device on both the indoor and outdoor coils. • Outdoor temperature 75°F • Superheat 55°F What is wrong with the system? - ANSWER-Undercharged. What will you get when a capillary tube is overcharged? - ANSWER-low superheat and high sub cooling What is the effect of a low charge on the switchover operations of a reversing valve? - ANSWER-Reversing valves are less likely to transfer if charge is low. A technician is working on a heat pump with a capacitor start-capacitor run compressor. On initial startup, the compressor hums momentarily and the shuts down on internal overload. What is the problem? - ANSWER-Too great a pressure difference on the compressor. A step down transformer has a rating of 40 VA. Its primary voltage is 120V with a secondary voltage of 24V. What is the maximum current draw of a load connected to this transformer? - ANSWER-1.7amps What does a bright red or orange glow from the resistance element in a duct heater indicate? - ANSWER-Flow of air is insufficient. What does the outdoor fan do during defrost on a heat pump and why? - ANSWER-The fan stops to minimize defrost time. What do bent vanes on a direct drive blower wheel in an air handler cause? - ANSWER-Loss in air flow, excessive motor wear, and increased noise. A split system heat pump is using thermostatic expansion valves. The system performs properly in heating but in cooling the compressor pumps down. What could this mean? - ANSWER-The power element of the indoor expansion valve has lost its charge. What condition can cause a reduction from design capacity in a heat pump? - ANSWER-Undersized vapor line. What is the result of excessive liquid line length or lift? - ANSWER-Flash gas. What symptom could a technician expect on a heat pump system in the cooling mode if the check valve is leaking internally? - ANSWER-Flooding of the indoor coil. Voltage across a closed contact in a 24V control circuit could indicate what? - ANSWER-Pitted or dirty contacts. What two checks typically made first on an electronic control? - ANSWER-Proper input voltage and proper output voltage. In a low voltage circuit, what does a corroded wire-to-terminal connection acts like? - ANSWER-An additional resistor. How should you test the continuity of a fuse? - ANSWER-Power off, fuse removed What is the first check made for most electrical troubleshooting? - ANSWER-Voltage check of the supply line. The following conditions exist in a circuit that supplies power to three parallel loads. One load is resistive One load is capacitive One load is inductive How do you find the total current? - ANSWER-The sum of the currents through each load. The technician is using an analog multimeter to check a run capacitor. With the meter set to ohms the needle swings toward zero and then slowly rises toward infinity. What does this tell the technician? - ANSWER-The capacitor charges and discharges. When should a technician test a hermetic compressor for a permanently open internal overload protector? - ANSWER-While its cool. What is defined as two or more switch contacts connected in a circuit, or set of circuits, to control a load? - ANSWER-Control String In order to troubleshoot a load controlled by a control string, what should the technician check first? - ANSWER-Proper voltage applied across the load. The technician suspects that an outdoor thermostat used to bring on auxiliary heat may be out of calibration. The thermostat is a close-on-fall type that is adjustable. What is one method for checking the thermostat calibration? - ANSWER-Manually rotate the shaft until the thermostat closes and compare the dial setting to an accurate outdoor temperature reading plus 10°F When must the installer must be certain to plumb the cabinet so its sides are vertical? - ANSWER-When changing out an evaporator coil. What is the recommended maximum external static pressure used for heating and cooling equipment with blowers for 5 ton of cooling or less? - ANSWER-0.1 in W.C When a balancing check of a newly installed duct what needs to happen? - ANSWER-Dampers should be open completely in all rooms. Why is operating sound is a consideration in the location of a condensing unit? - ANSWER-Because excessive noise could be disruptive to the customer A technician has determined a supply in a flexible duct system is leaking. What should be checked? - ANSWER-All connections inner and outer layers. What is sensible heat ratio? - ANSWER-sensible removed ÷ total heat removed Service site conditions are: • House feels "drafty" in cooling • 3½ ton split system • High supply face velocities • Ductwork is properly sized • Total CFM 1400 What does this indicate? - ANSWER-These readings indicate the system is operating normally but the supply registers are too restrictive When a wet bulb reading is very close to the dry bulb reading from the same instrument, what does this indicate? - ANSWER-Relative humidity is high. What measurements would be needed to properly evaluate a complaint of "drafty" operation with a heating system? - ANSWER-System TD, Drop, and Static Pressure What kind of energy does the condenser remove from the refrigerant? - ANSWER-Sensible heat and Latent heat Where does refrigerant boil? - ANSWER-In the Evaporator. What is the common suction line on a heat pump connected to? - ANSWER-The indoor coil and the compressor. What are the two generally used methods for changing capacity on demand in a heat pump? - ANSWER-Two speed compressor. Two stage thermostat What are the three things that happen when a heat pump is cycled into the defrost mode? - ANSWER-Reversing valve switches to cooling mode, Outdoor fan is shut off, and auxiliary heat is energized. What is a duct system that has a single trunk extending in one or two directions with many branch ducts? - ANSWER-Extended Plenum Duct System What is the effect on supply airflow when static pressure on the return is reduced? - ANSWER-Airflow will be increased. What is the voltage most often used to power the outdoor unit in a residential system? - ANSWER-240V Single Phase What happens if you increased suction pressure on a reciprocating compressor? - ANSWER-The capacity would decrease. The refrigerants typically used in residential and light commercial pumps have a storage life of? - ANSWER-An indefinite length of time. A restricted drier can cause what? - ANSWER-Lower than normal suction pressure What blower motor type is generally used on air handling equipment with capacities of 4,000 cfm or greater? - ANSWER-Belt driven with three phases. Electronic air cleaners can operate with internal voltages as high as? - ANSWER-5000V What is the purpose of a cross break on the flat sides of metal ductwork? - ANSWER-Increases rigidity and reduces vibration Whats the difference between a grille and a register? - ANSWER-Register is equipped with a air volume control device, grille is not. What is the purpose of a thermostatic expansion valve (TXT, TEV)? - ANSWER-Meter refrigerant flow to a coil to maintain superheater refrigerant leaving the coil What are Disc type temperature limit controls used for? - ANSWER-Protect auxiliary heat elements from overheating. How are disc type temperature limit controls reset? - ANSWER-By temperature. When the heat elements cool the switch resets. Where is the sensor of an outdoor ambient thermostat for a heat pump system typically installed? - ANSWER-In the entering air stream to the outdoor coil. A high pressure limit control is used for what? - ANSWER-To shut down a compressor if condensing pressure becomes excessive Where is a high pressure limit control installed? - ANSWER-Compressor discharge line. Where are low pressure limit controls installed? - ANSWER-The suction line of a heat pump. What is the purposes of a low pressure limit control? - ANSWER-Protect the compressor if suction pressure drops too low. To detect loss of charge. The timing specification of sequencers is often marked on the device using a code similar to what? - ANSWER-H1-24 C45-75 What is the specification for this sequencer code: H1-24 C45-75 - ANSWER-Contacts close 1-24 seconds after coil is energized and contacts open 45-75 seconds after coil is de-energized. What is the capability of electronic programmable room thermostat to reset the set point early so that the space temperature reaches a set temperature at a specific time called? - ANSWER-Computed recovery What is an important reason for using electronic controls? - ANSWER-They can make decisions based on many inputs. When using a double (dual) element time-delay fuse with a 20 amp motor, what is the maximum fuse size that should be used? - ANSWER-25amps According to fire protection codes, fire dampers should be used when? - ANSWER-In any air duct the passes through walls or partitions of a light commercial installation. What is balance point in a heat pump? - ANSWER-When the capacity, BTU, is the same rate as the heat loss of a structure. Do electric air cleaners remove odors? - ANSWER-No When should a suction line accumulator be used in a residential heat pump? - ANSWER-Only when recommended by the manufacturer if long refrigerant lines increase system charge over recommended maximum charge. The measurement of a heat pumps efficiency is often stated using its "Coefficient of Performance" or COP. What is the COP (Coefficient of Performance)of a heat pump? - ANSWER-Heat pumps heat output (watts) divided by its total electrical input (watts) What is a benefit in using electronic air cleaner? - ANSWER-Indoor Air Quality (IAQ) quality is improved. What is the thermal balance point of a dual fuel heat pump? - ANSWER-Outdoor conditions at which the capacity of auxiliary heat alone matches the heating load. What is the minimum circuit amp listed on a units' data plate is used to determine? - ANSWER-The max fuse or circuit breaker size. How are heat pumps particularly sized? - ANSWER-Based on the cooling load. What is an effective method of reducing sound when AHU is located in a closet? - ANSWER-Use Vibration isolators. When wiring a 20 amp FLA motor what is the minimum amp fuse or circuit breaker that should be used? - ANSWER-25amp How is the typical staging of a two stage HP system determined? - ANSWER-Use the deviation of the t-stat setting to determine when to engage each stage. What is the purpose of a sequencer in a HP with an AUX 20 kW electric heater? - ANSWER-Energize one or two elements and the blower then energize the other elements in timed intervals. In a HP (heat pump) circuit what is used to by-pass refrigerant flow around the metering device? - ANSWER-An open check valve. What is the most commonly used type of fan in residential systems? - ANSWER-The forward curve centrifugal fan. When is condensation on vapor lines a concern?when the lines are routed inside a wall. - ANSWER-When lines are routed inside a wall. In a single zone system; if a customer complains of feeling damp or sticky the cause could be what? - ANSWER-Unconditioned air being pulled into the duct work through holes in the duct. When performing indoor air balancing tests how should the t-stat should be set? - ANSWER-Should be set to bring on the indoor fan on mid-high speed. Most manufacturers recommend what size t-stat wire? - ANSWER-The smallest most allowable, 18AWG (All Weather Gauge) Where should you check voltage input to a compressor? - ANSWER-At the load side of the contactor. HP (Heat Pump) unit; 1st and 2nd stage appear to be calling, compressor runs but not electric heater, what is the problem? - ANSWER-Second stage is open. What do manufacturers recommend as the most acceptable method of attaching line sets to the AHU? - ANSWER-Utilizing brazing alloy. Why are there are more circuits in a HP (heat pump) outdoor coil than in an A/C outdoor coil? - ANSWER-To minimize refrigerant pressure drop. If a solenoid is vibrating or chattering, what is the cause? - ANSWER-Inefficient voltage or current. What is the coil of a potential relay connected to? - ANSWER-The common and start terminals of a compressor. When the load on a HP in cooling mode decreases, what happens to the suction pressure and the discharge pressure? - ANSWER-Suction pressure goes up and discharge pressure goes down. What is the purpose of an auto change over switch on a t-stat? - ANSWER-To allow automatic change over between heating and cooling. What is the result of undersized duct work? - ANSWER-High noise levels, high air quantity, and high static pressures. Where should the sensing bulb on a TXV be located to obtain an accurate refrigerant temperature on a horizontal suction line that is 1&1/8" or larger? - ANSWER-Should be located at 4 or 8 o'clock position on the line. What factors affects a customer's level of comfort? - ANSWER-Air movement Humidity Temperature What are the three processes that transfer heat energy? - ANSWER-Conduction Convection Radiation Heat transfer that occurs when substances of different temperatures are in contact with each other is called? - ANSWER-Conduction What effect does raising the pressure in a sealed system have on refrigerant? - ANSWER-The refrigerants boiling point increases. What is the primary danger to people near an accidental refrigerant release or spill? - ANSWER-Suffocation caused by the heavier refrigerant displacing oxygen in the air. The maximum temperature at which refrigerant may be stored is__________ when the container is no more than ________% full - ANSWER-125F, 80% Why is superheat necessary in a system that utilizes hermetic compression? - ANSWER-It ensures that dry vapor reaches the compressor so that mechanical damage does not occur When heat heat load on an evaporator increases, what is the effect on the system? - ANSWER-Suction pressure and discharge pressure both increase What type of energy is transferred when work is done in the condenser? - ANSWER-Both latent and sensible heat Which component pumps refrigerant through the system and raises the vapor temperature? - ANSWER-Compressor How are hermetic compressor motors cooled? - ANSWER-With suction vapor drawn from the evaporator Heat pump compressors sometimes run hotter than compressors used in cooling-only units because heat pump compressors _______. - ANSWER-Exhibit low refrigerant density at low suction When is crankcase heat most needed? - ANSWER-When the compressor is off. Work done on the refrigerant in the condenser is transferred as ________. - ANSWER-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? - ANSWER-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? - ANSWER-3.0 gpm per ton What tool should be used to shorten a capillary tube? - ANSWER-A triangular or knife-edge file Which pressure in a TXV is the opening pressure? - ANSWER-Bulb Pressure What effect does a low refrigerant charge have on reversing valve operation? - ANSWER-It increases the chance that the reversing valve will not be able to transfer properly Which of the following should be used to leak-test refrigerant tubing? - ANSWER-Dry nitrogen Of the motors commonly used in HVACR systems, which type has the lowest starting torque? - ANSWER-Shaded-Pole Motor Voltage supplied to a motor may vary from the rated voltage by _____% - ANSWER-d (+10%, -10%) What is one of the most important reasons for using electronic controls in HVACR systems? - ANSWER-They make decisions based on many inputs Hard-start kits are often needed on _______. - ANSWER-Reciprocating compressors used with TEVs A 24v transformer with a 40 VA rating can safely operate with a current of ________. - ANSWER-1.67 Amps According to Ohm's Law, what will happen if voltage to a heater element is increased 10%? - ANSWER-The current draw will increase by 10% When the airflow through an electric heater is insufficient, the technician will observe_______. - ANSWER-Heater elements glowing red or orange Which combination of measurements indicates an open heater element? - ANSWER-Voltage to the heater with no current draw through the heater elements What internal voltage is likely to be measured in an electronic air cleaner? - ANSWER-5000V What problem is likely to occur if a proper trap is not used on the condensate drain for a pull-through unit? - ANSWER-Condensate water will not drain properly and will back up above the primary drain What issues affect the decision to use a running trap on a condensate line at the evaporator coil? - ANSWER-Running traps do not allow for the proper drainage of condensate water The auxiliary drain line from an overflow pan must _________. - ANSWER-be terminated at some conspicuous location so that an overflow is readily noticed Which of the following brazing materials is acceptable for use on a refrigerant piping? - ANSWER-Brazing allow with an approved flux Why must you exercise caution when bending soft-drawn refrigerant tubing? - ANSWER-Any distortion of the tubing diameter creates a restriction to refrigerant flow that reduces system capacity What voltage is measured between any two hot legs on a 3-phase 240V distribution panel? - ANSWER-240V 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 220V, and the current draw of the furnace is 47 A? - ANSWER-1,170 CFM Note: CFM = Btuh / (1.08 x TD) Btuh = W x 3.413 W = V x A What is an example of a power - passing device? - ANSWER-Fan Switch In wiring diagrams, solid lines usually indicate ______. - ANSWER-factory-installed line-voltage In wiring diagrams dashed or dotted lines usually indicate _____. - ANSWER-field-installed wiring Exposure to an electric current of ___ mA can be fatal if it lasts for one second or more. - ANSWER-100 to 200 mA The use of ground fault circuit interrupter (GFCI) is especially important when ________. - ANSWER-work is being done on wet surfaces. A good fuse will yield a reading of ________on an ohmmeter. - ANSWER-0 Ω Any individual load on a 24 V control circuit should draw a measurable current of ______ A. - ANSWER-less than 1Amp Black and white leads on a step-down transformer indicate a _____. - ANSWER-120-V ac primary Note: Typical color coding: 120 V: black and white primary, yellow and blue secondary 230 V: red and black primary, yellow and blue secondary A resistance reading of 0 Ω across a coil indicates that the coil is _____. - ANSWER-shorted A small voltage reading across a closed set of contacts in an energized circuit indicates that the _______. - ANSWER-contacts are pitted. A resistance reading of infinity across the "R" terminal and "S" terminal of a compressor motor indicates a(n) _________. - ANSWER-open motor winding An acceptable capacitance reading for a run capacitor is _____ the microfarad rating printed on the capacitor. - ANSWER-plus or minus 10% of. How may CFM per ton of cooling? - ANSWER-400CFM per ton How many BTUh per ton of cooling? - ANSWER-12,000BTUH per ton What is measured to determine the total resistance to airflow in a ductwork system? - ANSWER-External static pressure at the air handler or furnace 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? - ANSWER-32,080 Btuh Btuh = W x 3.413 W = V x A What is the total CFM: Voltage: 240V Amps: 40A Return air: 70 Supply air: 105 - ANSWER-867 cfm cfm = (voltage x current x 3.413) / (temperature rise x 1.08) What is the recommended face velocity for air leaving a supply register? - ANSWER-700 ft/min Temperature readings taken 6 in. from the compressor discharge line should never exceed ___________ F. - ANSWER-225°F A system should operate at least _____ before heat measurements are taken - ANSWER-20 minutes What gas should be purged through a refrigerant circuit to prevent the formation of oxides whenever brazing is being done? - ANSWER-Dry Nitrogen What certification is required before a technician is permitted to work on air conditioning and heat pump systems? - ANSWER-EPA Section 608 certification