HVAC/R ELECTRICITY FINAL EXAM STUDY GUIDE
A capacitor analyzer is designed to measure the; ... capacitance of a capacitor. capacitive resistance of a capacitor. capacitor voltage percentage of leakage.
A
A device with overload protection used to control a motor is a; ... direct on-line starter. motor relay. remote sensing contactor. selenium rectifier.
A
A diode is used to; ... control the direction of electron flow. convert DC current to AC current. increase or decrease frequency. increases inductive reactance.
A
A parallel circuit contains an 18-ohm and 9-ohm resistor. The total resistance equals; ... 6 ohms 8 ohms. 10 ohms 27 ohms.
A
In the schematic, the coil on line #12 controls the; ... blower motor relay. fan switch. thermostat. transformer.
A
In the schematic, what voltage would be found acriss the contacts in line #11? (Assume the thermostat is in the closed position and the fan is set to Auto.) ... 0 volts 120 volts 240 volts 480 volts
A
Resistance can be calculated by; ... E/l. F2 x W. I/E WIE.
A
When testing a motor winding for resistance, the following measurements are recorded: common to run 4 ohms, common to start 6.2 ohms, run to start 10.2 ohms, common to ground 20.4. These recorded measurements indicate a/an; ... good safety ground. grounded condition. locked rotor condition. open in the winding.
B
A direct digital control (DDC) is a/an; ... digital control for controlling the electron flow in a series circuit. digital control for controlling the electron flow in a parallel circuit. electronic control that must be manually adiusted. electronic control used for equipment operation and monitoring.
D
A drawing that illustrates where components are located and the wiring between these components in small appliances is a/an; ... ladder diagram outside diagram. pictorial diagram. schematic diagram.
D
What can be done to provide a common wire to an electronic thermostat when the existing cable cannot be replaced or when an additional wire cannot be installed? ... A diode and a DC capacitor are wired in series with the fan circuit and the common terminal. A diode and an AC capacitor are wired in series with either the heating or cooling circuit and the common terminal. The common is made through the "C" terminal on the system compressor. An add-a-wire accessory can be used to take the place of terminals "y" and "G"
D
What term is used to describe the output side of a transformer? ... High inductive side Low inductive side Primary side Secondary side
D
When resistors are wired in parallel the; ... current through any one resistor will be the same as the total circuit current. total resistance is determined by adding the values of each resistor. voltage drop across each resistor will be the same as the applied source voltage. voltage drop across each resistor will depend on the value of each resistor.
D
When troubleshooting the A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and condenser fan are not running. The blower motor is running. This could be caused by; ... a de-energized BR (line 8). an energized CCH. an energized contactor coil (line #11). an open HP, LP, overloads, or oil pressure switch (line #11).
D
When troubleshooting the AVC system in the sond condenser fan motors are shotowing conditions are found. The thermostat contacts are closed. The compressor and confrom ere Autolors are short cycling. The blower motor is not tumming. When the fan switch at the thermostat is moved from the AUTO position to the FAN ON position, the blower runs. This could be caused by; ... a blown fuse on line # 10. a faulty blower relay coil. a faulty contactor. a faulty thermostat - AUTO / FAN ON switch.
D
Which device changes the pressure signal in an electronic oil safety switch to an electrical signal? ... Electronic processor The bellows The circuit board Transducer
D
Which of the following is generally considered to be within the maximum allowable (+/-) supply voltage variation for a 230-volt supply? ... 184 to 242 volts 196 to 245 volts 207 to 276 volts 219 to 242 volts
D
Which of the following letter is the representation for impedance in an AC circuit? ... W X Y Z
D
Which of the following materials would be used as a semi-conductor? ... Aluminum Copper Mercury Silicon
D
With a motor running at full load, voltmeter leads are placed on L1 and T terminals of the contactor. The voltmeter indicates no measurable voltage. This is an indication of, ... excessive resistance in the contacts. good clean contacts no voltage to the motor. this is not a valid test.
D
Current flow will increase when; ... current flow is the same as voltage. resistance increases. voltage decreases. voltage increases.
D
When current lows in a two-wire circuit (such as 120 volts) if a camp on amp meter is clamped around both wires what measurement would you expect? ... Double the amps due to reversing the magnetic field, Half the amperage due to reversing the magnetic field. The same reading as a one wire circuit. Zero amps due to cancellation of the two fields.
D
A multimeter set to measure resistance should never be connected to a/an; ... charged capacitor until it has been discharged coil or a winding of a compressor. motor that has a grounded condition. resistor until it has been checked by other means.
A
A solenoid valve coil operates on the principle of; ... electromagnetism. pressure differential. temperature differential. time and temperature.
A
A three-phase load requires a minimum of; ... three supply lines three supply lines and a neutral. two supply lines. two supply lines and a ground.
A
A transformer has 1,000 turns of wire in the primary coil and 500 turns in the secondary coil. If 120-volts are applied, the output voltage will be; ... 60 volts. 120 KV 240 volts. 620 volts.
A
An electron has: ... a negative charge. a neutral charge. A positive charge. no charge.
A
Any material that will readily release electrons is called a/an; ... conductor. insulator. neutron. resistor.
A
Circuit breakers and fuses are primarily used for; ... protection from an overload of current. protection of over impedance to a condensing unit. C protection of impedance for inductive loads. switches used as protection devices.
A
Cooling anticipation is performed by the thermostat; ... during the off cycle. during the on cycle. in minutes of compressor off time. minutes squared of compressor run time.
A
How much resistance must be placed in a 120-volt circuit to limit the current to 2 amps? ... 60 ohms. 118 ohms 120 ohms 240 ohms
A
In a series circuit, the voltage drop acros each resistance (a) will; ... add up to equal the source voltage. add up to the total resistance. depend on the current to each resistor. depend on the wire gauge.
A
In the schematic, if the fuse in L2 is blown the; ... blower motor will continue to operate. blower motor will single phase and burn-out. compressor will continue to operate. transformer will be de-energized
A
In the schematic, the coil on line #11 does NOT control; ... the blower motor. the compressor. the condenser fan motor. the crankcase heater.
A
In the schematic, what voltage would be found acriss the contacts in line #8? (Assume the thermostat is in the closed position and the fan is set to Auto.) ... 0 volts 120 volts 240 volts 480 volts
A
In the schematic, what voltage would be found from terminal R to terminal G on ther thermostat? ... 0 volts 120 volts 240 volts 480 volts
A
In the schematicwhat voltage wold be found ares the us in ine #10? ... 0 volts 120 volts 240 volts 480 volts
A
On a good single-phase compressor motor, which winding terminals have the highest resistance? ... Common to ground Common to start Run to ground Run to start
A
Referring to the diagram, which is the symbol for a pressure switch that closes on pressure rise? ... A B C D
A
Relays are generally used to control inductive loads ranging between; ... 1-15 amps 16-30 amps. 31-50 amps 51-100 amps.
A
The correct formula for determining wattage in an electrical circuit is; ... W= Ex | W=E/R W=Ex R W=I/R
A
The most common type of transducer used with HVAC equipment creates a signal based on; ... pressure the specific gravity of the refrigerant. Time turbulence.
A
Thre (3) resistors, each 300 ohms, are wired in parall. The total resistance equals; ... 100 ohms 300 ohms. 600 ohms. 900 ohms.
A
When testing the windings of a single-phase motor, the; ... common to run terminals will show the lowest resistance. common to start terminals will show the lowest resistance. pair of terminals with the highest resistance will indicate that the other terminal is the start. start to run terminals will show the lowest resistance.
A
When the temperature of a negative temperature coefficient (NTC) thermistor increases, its resistance will; ... Decrease. Increase increase proportionately to the Delta T. remain the same
A
Which of the following motors has the highest energy efficiency? ... ECM PSC SIRC Shaded Pole
A
A parallel circuit consists of three resistors [R1 = 30 ohms R2 = 15 ohms R3 = 10 ohms] if the current through 52 - amares, hat is the source voltage? ... 20 volts 60 volts 120 volts 220 volts
B
Capacitors are always connected to the start winding; ... in parallel. in series. through a diode. through a relay.
B
Capacitors are rated in; ... amps & volts. microfarads & volts. microfarads & watts volts & ohms.
B
Contactors are rated according to the maximum amperage through the; ... Coil Contacts Fuse Thermostat
B
Current flow is the; flow of voltage in a circuit. flow of electrons in the circuit. impedance of a circuit. inductive reactance of the circuit.
B
Excessive current can be caused by; ... an open circuit. a short circuit. an undersized fuse. oversized wiring.
B
Fuses are sized by; ... amps & watts. volts & amps volts & watts. watts & ohms.
B
How many diodes are used to make a bridge rectifier connected to a center tap 3-wire transformer? ... 1 2 3 4
B
In electrical wiring, a black colored witre in an aemating curent crout usualy indicates the: ... ground conductor. hot conductor. neutral conductor. safety ground.
B
In the schematic, the crankcase heater will operate; ... at all times. when the compressor is off. when the compressor is on. when the oil pressure switch is on.
B
In the schematic, what voltage would be found from terminal Y to the output side of the coil on line #11? ... 0 volts 120 volts 240 volts 480 volts
B
On a split-type heat pump system with an electronic data type control, what is the minimum numbers of wires that need to be run between the indoor unit and the thermostat? ... 2 wires 4 wires 6 wires 8 wires
B
Referring to the diagram, which is the symbol for a heating thermostat? ... A B C D
B
The direction of rotation of a single-phase induction motor is determined by the; ... direction of current flow through the run winding. direction of current flow through the start winding. number of poles in the motor. voltage applied to the start winding.
B
The symbol for current is; ... E. I. R. W.
B
The voltage to ground of a "High leg" on a three-phase open Delta system will be approximately ... 120 208 220 240
B
To change direction of rotation of a three-phase motor; ... change the position of all three supply wires. change the position of any two supply wires. the motor must be replaced. the rotation of three phase motors cannot be changed.
B
Voltage can be calculated by; ... I/R. Ix R R/I. W/R.
B
What connects to teminals 1, T2, & T3 on a contactor or motorstater? ... Coil connections and ground Load connections. Power supply connections Start / stop leads
B
When checking the windings of a three-phase motor; ... all three terminals should show different readings. all three terminals should show the same resistance. the pair of windings with the highest resistance will indicate the other is common. the resistance of one winding should be the sum of the other two
B
When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance will; ... decrease. increase. increase proportionately to the Delta T. remain the same.
B
When troubleshooting the A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and condenser fan motors are short cycling. The blower motor is not running. This could be caused by; ... a blown fuse on line #10. a faulty blower motor or blower relay. a faulty coil on line #11 an open transformer.
B
Which function of a digital multimeter is used to bench check a motor for shorts or open windings? ... Amperage Resistance Volts Watts
B
Which of the following would be considered an inductive load? ... electric heat strip electric motor solid state relay start capacitor
B
The color of the safety ground wire is usually; ... black or white. green or bare. red or white. white or bare.
B
If contacts on a 30-amp contactor become badly pitted, it is acceptable to; ... file the contacts replace the contacts or contactor. replace the control with a solid-state general-purpose relay. sand the contacts
B
What is the minimum number of wires required between two mechanical start/stop push button controls? ... 1 2 3 4
B
2.1 kilowatts (KW is equal to; ... 21 watts. 210 watts. 2,100 watts. 21,000 watts.
C
A Wi-Fi thermostat communicates with the network by the; ... name assigned to the thermostat by the contractor. name of the thermostat from the manufacturer. thermostat's IP and/or Mac address. thermostat's model and serial number.
C
A thermocouple can; ... be used to power a shaded pole motor. generate a small AC electrical current. generate a small DC electrical current. generate up to 1 volt.
C
A transformer has 1,000 turns of wire in the primary coil and 2000 turns in the secondary coil. If 120-volts are applied, the output voltage will be; ... 60 volts. 120 KV 240 volts. 620 volts.
C
Heatng anticipation is performed by a mechanical thermostat; ... by the off time of the fumace, in minutes. by the run time of the fumace, in minutes. during the off cycle. during the on cycle.
C
If a 24-volt, 20-ohm, low-voltage contactor coil were wired in series with a 24-volt, 200-hm control relay coil what would the result be? ... Both the contactor and control relay would operate. Neither the contactor nor control relay would operate. Only the control relay would operate. Only the contactor would operate
C
If the conductor in an AC circuit is wound into a coil, the resulting EM opposes the supply voltage This opposition is called; ... capacitive reactance. Conductance. inductive reactance. influence.
C
Impedance is the measurement of the; ... amperage in a circuit. electrical pressure in a circuit. opposition to the flow of alternating current through a circuit. voltage applied to the circuit.
C
In the schematic, what voltage would be found across L1 to L2? ... 0 volts 120 volts 240 volts 480 volts
C
In the schematic, what voltage would be found across the condenser fan motor? ... 0 volts 120 volts 240 volts 480 volts
C
In the schematic, what voltage would be found across the transformer primary? ... 0 volts 120 volts 240 volts 480 volts
C
One horsepower is equal to; ... 3.415 watts. 208 watts. 746 watts. 1,200 watts.
C
Single-phase motor speed is determined by the; ... circumference of the rotor. number of coils in the stator. number of stator poles. supply voltage.
C
The symbol for a pressure switch that opens on pressure rise is represented by diagram ... A B C D
C
To discharge a capacitor prior to testing with a digital multimeter; ... touch the terminals with your bare fingers. use a screwdriver across the capacitor terminals use a 15,000 or 20,000 ohm, 2 to 5-wait resistor across the terminals. use a 5,000 ohm, 2 to 5-watt resistor across the terminals.
C
A step-up transformer increases; ... amperage. power. resistance. voltage
D
An electronically commutated motor (ECM) used in an air-handler is designed to; ... have low starting torque maintain a constant velocity. operate at a lower static pressure than axial fan motors. provide proper air flow under various conditions.
D
How is the common on electronic thermostats obtained when there are only 4 wires (R, G, W, and Y) from the old heating and cooling thermostat? ... The common is made through the back EMF of the fan relay circuit. The common is made through the cooling circuit when the thermostat is et for cooling and through the heating circuit when the thermostat is set for heating The common is made through a diode and DC capacitor wired in series with the indoor fan relat The thermostat references common through an inactive circuit
D
How many diodes are used to make a bridge rectifier connected to a 2-wire transformer? ... 1 2 3 4
D
How many watts of power are used by a heater operating at 460-volts and drawing 5-amps? ... 5 watts 92 watts 460 watts 2,300 watts
D
Like charges; ... are negative. are positive. attract one another. repel each other.
D
Resistance is; ... electrical pressure causing voltage flow. enabled amperage flow. opposition to alternating current only. opposition to current flow.
D
The capacitor start-capacitor run (SCR) motor provides; ... high running and low starting torque. high running and medium starting torque. high starting and high running torque. medium running and high starting torque.
D
The synchronous speed of a two pole, 60-Hz single-phase motor is; ... 1500 гр 1800 гр 3450 гр 3600 гр
D
The total resistance of a parallel circuit will be; ... equal to the largest resistance equal to the smallest resistance. less than the smallest resistance. the sum of all resistances.
D
Three (3) defrost heaters, each 15 ohms, are wired in parallel to a 120-volt power supply. How many watts of power will be used? ... 8 watts. 24 watts 1800 watts. 2880 watts.
D
Transformers are rated according to; ... ohms at the primary. ohms at the secondary. volt-amps (VA) at the primary: volt-amps (VA) at the secondary.
D
