HVAC electrical test Flashcards by Joel Jorgensen

What is current flow?

The flow of electrons in the circuit.

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What is impedance?

Opposition to alternating current flow?

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Like charges will..

Repel each other.

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Any material that will readily release electrons is called?

A conductor

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The symbol for current is?

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Electricity can produce

Heat, light, magnetism

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The safety ground conductor is usually color coded?

Green

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An electron has?

A negative charge

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What is resistance?

Opposition to current flow

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How many watts of power are used by a heater operating at 460 volts and drawing 5 amps?

2300

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What type of meter uses it’s own battery?

Ohmmeter

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In electrical wiring, a black colored wire usually indicates….

The hot conductor

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How are fuses sized?

Amps and volts

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Two 120 volt motors are wired in a series, one is a 60 watt motor, the other is a 4 watt motor. The result would be…?

Neither motor would operate normally

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What would be the result of three defrost heaters, each 12.5 ohms, wired in a series to a 115 volt power supply, it the heaters were to supply a 360 watt heating load?

Heaters do not energize

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What is generally considered to be the maximum allowable (+ or -) supply voltage variation?

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Capacitors are rated in…

Microfarads and volts

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When testing a capacitor with an analog ohmmeter, the needle on the meter should..

Deflect towards zero then return to infinite reading.

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What is the term used to describe the output side of a transformer?

Secondary side

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One horsepower is equal to _______ watts.

746

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How much resistance must be placed in a 110 volt circuit in order to limit the current to 2 amps?

A. 55 ohms
B. 110 ohms
C. 30 ohms
D. None of the above

55 ohms

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A parallel circuit contains a 18 ohm and a 9 ohm resistor. The total resistance equals…

A. 6 ohms
B. 27 ohms
C. 8 ohms
D. 10 ohms

6 ohms

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In a series circuit, the voltage drop across each resistance (load) will…

A. Always add up to equal the source voltage.
B. Depend on the value of each resistor.
C. Depend on the current flow in the circuit.
D. All of the above

All the above

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The total resistance of a parallel circuit will be…

A. The sum of all resistances
B. Equal to the largest resistance
C. Equal to the smallest resistance
D. Less than the smallest resistance.

Less than the smallest resistance

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Which of the following statements about current is true? A. Current flow is the same as voltage B. Current flow will increase when voltage increases. C. Current flow will increase when resistance increases. D. Current flow will decrease when voltage increases.

Current flow will increase when voltage increases.

When resistors are wired in parallel... A. The current through any one resistor will be the same as the total circuit current. B. The voltage drop across each resistor will be the same as the applied source voltage. C. The voltage drop across each resistor will depend on the value of each resistor. D. The total resistance is determined by adding the values of each resistor.

The voltage drop across each resistor will be the same as the applied source voltage.

``` Which of the following is equal to 2.1 KV? A. 21 volts B. 210 volts C. 2100 volts D. 21000 volts ```

2100

``` Which of the following is equal to 100 milliamps? A. 1.0 amperes B. 10.0 amperes C. 0.10 amperes D. 0.01 amperes ```

0.10 | each amp is equal to 1000 milliamps

A capacitor analyzer is designed to.. A. Read power factor percentage B. Diagnose an open or shorted capacitor. C. Read the microfarad rating of a capacitor. D. All of the above

Read the microfarad rating of a capacitor

A 240 volt, 3 wire circuit can be split into two 120 volt circuits. True or false?

False

``` The meter on a house measures the _______ passing through it. A. Voltage B. Amperage C. Wattage D. Resistance ```

Wattage

A three phase system requires a minimum of the three supply lines to the three phase load. True or false?

True

``` Which of the following is the correct formula for determining wattage in an electrical circuit? A. W=ExI B. W=E/R C. W=I/R D. W=ExR ```

W=ExI

A parallel circuit consists of three resistors. R=30ohms R2=15ohms R3=10ohms If the current through R2=4 amperes, what is the source voltage? A. 20 volts B. 60 volts C. 120 volts D. 220 volts

60 volts

``` Three 300 ohm resistors are wired in parallel. The total resistance equals... A. 100 ohms B. 300 ohms C. 600 ohms D. 900 ohms ```

100 ohms

``` Amperes can be calculated by... A. E divided by R B. W divided by E C. The square root of W divided by R D. All of the above ```

All of the above

``` Resistance can be calculated by... A. E divided by I B. W divided by E C. E squared times W D. All of the above ```

E divided by I

``` Voltage can be calculated by... A. I divided by R B. R divided by I C. I times R D. All of the above ```

I times R

``` An ohmmeter should never be connected to... A. A resistor B. A coil C. A motor winding D. A live circuit ```

A live circuit

``` Three resistors are wired in series. Each has a value of 300 ohms. What is the total resistance of the circuit? A. 100 ohms B. 150 ohms C. 600 ohms D. 900 ohms ```

900 ohms

Three resistors are wired in a parallel. Two of the resistors have a value of 12 ohms, one resistor has a value of 6 ohms. What is the total resistance of the circuit? A. 30 ohms B. 18 ohms C. 3 ohms D. It's not possible to wire resistors of different values in parallel.

3 ohms

``` A transformer has 1000 turns of wire in the primary coil and 500 turns in the secondary coil. If 120 volts are applied, the output voltage will be... A. 120kv B. 620 volts C. 60 volts D. 240 volts ```

60 volts

``` A transformer has 1000 turns of wire in the primary coil and 2000 turns in the secondary coil. If 120 volts are applied, the output voltage will be... A. 120kv B. 620 volts C. 60 volts D. 240 volts ```

240 volts

``` Impedance in a circuit is the result of... A. Pure resistance B. Inductive reactance C. Capacitive reactance D. All of the above ```

All of the above

``` When current flows, a ______ is produced around the conductor. A. Magnetic field B. Dielectric transmitter C. Short circuit D. Worm hole ```

Magnetic field

``` If the conductor in an AC circuit is wound into a coil, the resulting EMF opposes the supply voltage. This opposition is called... A. Capacitive reactance B. Inductive reactance C. Conductance D. Influence ```

Inductive reactance

``` A capacitor opposes current flow in a circuit. This opposition is called... A. Capacitance reactance B. Inductive reactance C. Conductance D. Influence ```

Capacitive reactance

``` A ___________ may be used on a single phase induction motor to disconnect the start winding after the motor starts. A. Centrifugal switch B. Amperage relay C. Potential relay D. Any of the above ```

Any of the above

Direction of rotation of a single phase induction motor is determined by... A. The direction of current flow through the start winding. B. The direction of current flow through the run winding. C. The number of poles in the motor. D. All of the above

The direction of the current flow through the start winding

Single phase motor speed is determined by the... A. Size of the wire used in the windings B. Number of stator poles C. Supply voltage D. All of the above

Number of stator poles

``` The capacitor start-capacitor run (CSCR) motor... A. Provides high starting torque B. Provides high running torque C. Both A and B D. Neither A nor B ```

Both A and B

To change direction of rotation of a three phase motor... A. The motor must be replaced B. Change the position of all three supply wires C. Change the position of any two supply wires D. The rotation of three phase motors cannot be changed

Change the position of any two supply wires

``` Capacitors are always connected ____________ to the start winding. A. Parallel B. In series C. Through a relay D. Through a diode ```

In series

``` What meter is used to bench check a motor for shorts or open windings? A. Ohmmeter B. Voltmeter C. Ammeter D. Wattmeter ```

Ohmmeter

``` A solenoid valve operates on the principle of.... A. Pressure differential B. Temperature differential C. Electromagnetism D. All of the above ```

Electromagnetism

When checking the windings of a three phase motor... A. All three terminals should show different readings B. The pair with the highest resistance will indicate the other is common C. All three terminals should show the same resistance D. It is usually cheaper to replace a three phase motor than to test it.

All three terminals should should show the same resistance

``` When testing the windings of a single phase motor, technician 1 says that the common and run terminals show the lowest resistance. Technician 2 says that the pair of terminals with the highest resistance will indicate that the other terminal is the common. Who is correct? A. Technician 1 B. Technician 2 C. Both technician D. Neither technician ```

Both technicians

``` Technician 1 says that an open transformer coil is indicated by a reading of 0 ohms on an ohmmeter. Technician 2 says that a shorted transformer coil is indicated by a reading of infinity on an ohmmeter. Who is correct? A. Technician 1 B. Technician 2 C. Both technicians D. Neither technician ```

Neither technician

``` A step up transformer increases... A. Power B. Voltage C. Resistance D. Amperage ```

Voltage

``` Transformers are rated according to... A. VA at the primary B. VA at the secondary C. Ohms at the primary D. Ohms at the secondary ```

VA at the secondary

``` Utility companies usually supply residential homes with _________ service. A. 115v, single phase, three wire B. 240v, single phase, three wire C. 240v, three phase, three wire D. 480v, three phase, three wire ```

240v, single phase, three wire

``` The terminals T1, T2, & T3 are located at the _________ of a conductor. A. Top B. Bottom C. Middle D. Side ```

Bottom

``` Fuses are used to protect... A. People B. Loads C. Wires D. Switches ```

Wires

``` Over-current can be caused by... A. Ground faults B. Overload C. Short circuit D. All of the above ```

All of the above

``` A device used to control a motor is a... A. Relay B. Contactor C. Line starter D. All of the above ```

All of the above

``` Relays used in the HVAC industry are generally used to control loads up to ____ amps. A. 100 B.10 C. 25 D. 50 ```

``` Contactors are rated according to the maximum amperage through the... A. Coil B. Contacts C. Thermostat D. Fuse ```

Contacts

``` How many switches can be connected to a contactor coil control circuit? A. 1 B. 2 C. 3 D. Unlimited ```

Unlimited

If contacts become dirty or pitted, it is acceptable to sand or file them as a permanent repair. True or false?

False

The thermal overload contacts on a line starter are usually ______ reset. A. Manual B. Automatic

Manual

``` The _________ drawing illustrates where the components are located on the appliance. A. Pictorial B. Schematic C. Ladder diagram D. Outside ```

Pictorial

Single phase motors are more efficient than three phase motors. True or false?

False

``` In a single phase motor, which winding has the most resistance? A. Start B. Run C. Ground D. They are all equal ```

Start

When testing a motor with an ohmmeter, one winding shows a 1000 ohm continuity to the motor frame. This is an indication of a good safety ground. True or false?

False

``` With a motor running at full load, voltmeter leads are placed on each side of the relay contacts. The voltmeter gives no measurable voltage. This is an indication of... A. No voltage to the motor B. Excessive resistance in the contacts C. Good clean contacts D. This is not a valid test ```

Good clean contacts

When the temperature of a negative temperature coefficient (NTC) thermistor increase, its resistance will... A. Increase B. Decrease C. Remain the same

Decrease

When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance will... A. Increase B. Decrease C. Remain the same

Increase

``` A transducer can create a signal based on a form of energy such as... A. Pressure B. Heat C. fluid flow D. All of the above ```

All of the above

A thermocouple can... A. Generate a small electrical current, depending on temperature B. Become hot or cold when current is passed through, depending on the direction of current. C. Both A and B D. Neither A nor B

Generate a small electrical current, depending on temperature

To discharge a capacitor prior to ohmmeter testing... A. Use a screwdriver to short across the terminals B. Use a 20,000 ohm resistor to short across the terminals C. Touch the terminals with your bare fingers D. Capacitors do not need to be discharged prior to testing

Use a 20,000 ohm resistor to short across the terminals

When replacing a capacitor... A. Use a replacement with the same value as the original B. If a duplicate of the original is not available, a capacitor that is up to 10% over capacity is OK C. Never use a capacitor that is under capacity D. All of the above

All of the above

``` The synchronous speed of a 4 pole, 60 Hz single phase motor is... A. 3600 rpm B. 1500 rpm C. 3450 rpm D. 1800 rpm ```

1800 rpm | 120 volts X 60Hz __________________ 4 # of poles

Compressing or decompressing certain kinds of crystals produce a ______ voltage. A. Magnetoelectric B. Photoelectric C. Piezoelectric D. thermoelectric

C. Piezoelectric

The two basic types of variable resistors are the _______ and the _______. A. AC resistors, DC resistors B. Carbon resistor, wire-wound resistor C. One-lug resistor, two-lug resistor D. Rheostat, potentiometer

D. Rheostat, potentiometer

Witch of the following materials is best known conductor of electric current? A. Copper B. Gold C. Silver D. Tungsten

C. Silver