Podcast
Questions and Answers
What is current flow?
What is current flow?
The flow of electrons in a circuit
What is impedance?
What is impedance?
Opposition to alternating current
Like charges will
Like charges will
Repel each other
Any material that will readily release electrons is called:
Any material that will readily release electrons is called:
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The symbol for current is:
The symbol for current is:
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Electricity can produce:
Electricity can produce:
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The safety ground conductor is usually colored:
The safety ground conductor is usually colored:
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An electron has:
An electron has:
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Which of the following materials would be best suited for use as a semi-conductor?
Which of the following materials would be best suited for use as a semi-conductor?
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Which of the following meters must use internal power to check a load or circuit?
Which of the following meters must use internal power to check a load or circuit?
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What would be the result if a 24 volt, 20 ohm contactor coil was wired in series with a 24 volt, 200 ohm control relay?
What would be the result if a 24 volt, 20 ohm contactor coil was wired in series with a 24 volt, 200 ohm control relay?
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Three defrost heaters, each 15 ohms, are wired in parallel to a 120 volt power supply. How many Watts are consumed?
Three defrost heaters, each 15 ohms, are wired in parallel to a 120 volt power supply. How many Watts are consumed?
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When testing a capacitor with an analog or digital ohmmeter, the meter should:
When testing a capacitor with an analog or digital ohmmeter, the meter should:
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How much resistance must be placed in a 120 volt circuit to limit the current to 2 amps?
How much resistance must be placed in a 120 volt circuit to limit the current to 2 amps?
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What is resistance?
What is resistance?
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In electrical wiring, a black colored wire indicates:
In electrical wiring, a black colored wire indicates:
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How many watts are used by a heater operating on 460 volts and drawing 5 amps?
How many watts are used by a heater operating on 460 volts and drawing 5 amps?
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How are fuses sized?
How are fuses sized?
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What is generally considered the maximum allowable supply voltage variation?
What is generally considered the maximum allowable supply voltage variation?
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Capacitors are rated in:
Capacitors are rated in:
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What is the term used to describe the output side of a transformer?
What is the term used to describe the output side of a transformer?
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One horsepower is equal to _____ watts.
One horsepower is equal to _____ watts.
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A parallel circuit contains an 18 ohm and a 9 ohm resistor. What is the total resistance?
A parallel circuit contains an 18 ohm and a 9 ohm resistor. What is the total resistance?
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In a series circuit, the voltage drop across each load will:
In a series circuit, the voltage drop across each load will:
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Which of the following is equal to 2.1kW?
Which of the following is equal to 2.1kW?
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A capacitor analyzer is designed to check:
A capacitor analyzer is designed to check:
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On an electronic oil safety switch, what changes the pressure signal to an electrical signal?
On an electronic oil safety switch, what changes the pressure signal to an electrical signal?
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A three-phase load requires a minimum of
A three-phase load requires a minimum of
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An electronically commutated motor (ECM) is designed to:
An electronically commutated motor (ECM) is designed to:
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Resistance can be calculated by:
Resistance can be calculated by:
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The total resistance in a parallel circuit will be:
The total resistance in a parallel circuit will be:
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Which of the following statements about current is true?
Which of the following statements about current is true?
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When resistors are wired in parallel:
When resistors are wired in parallel:
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Which of the following is equal to 100 milliamps?
Which of the following is equal to 100 milliamps?
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The meter on a house measures the ____ passing through it.
The meter on a house measures the ____ passing through it.
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What is the correct formula for determining wattage?
What is the correct formula for determining wattage?
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A parallel circuit consists of three resistors; R1 = 30 ohms, R2 = 15 ohms, R3 = 10 ohms. If the current through R2 = 4 amps, what is the source voltage?
A parallel circuit consists of three resistors; R1 = 30 ohms, R2 = 15 ohms, R3 = 10 ohms. If the current through R2 = 4 amps, what is the source voltage?
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Three 300 ohm resistors are wired in parallel. What is the total resistance?
Three 300 ohm resistors are wired in parallel. What is the total resistance?
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Amps can be calculated by:
Amps can be calculated by:
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Voltage can be calculated by:
Voltage can be calculated by:
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An ohmmeter should never be connected to a:
An ohmmeter should never be connected to a:
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Which of the following would be considered an inductive load?
Which of the following would be considered an inductive load?
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The voltage to ground of a high leg or 'stinger leg' on a three-phase open delta system will be approximately:
The voltage to ground of a high leg or 'stinger leg' on a three-phase open delta system will be approximately:
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Which of the following is the symbol for impedance?
Which of the following is the symbol for impedance?
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What amperage measurement would you expect if you clamped your meter around both wires in a two-wire circuit?
What amperage measurement would you expect if you clamped your meter around both wires in a two-wire circuit?
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A diode is used to?
A diode is used to?
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Three resistors are wired in parallel. Two have a value of 12 ohms, one of 6. What is the total resistance?
Three resistors are wired in parallel. Two have a value of 12 ohms, one of 6. What is the total resistance?
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A transformer has 1000 turns on the primary side and 500 on the secondary. What is the output if the input is 120v?
A transformer has 1000 turns on the primary side and 500 on the secondary. What is the output if the input is 120v?
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A transformer has 1000 turns on the primary side and 2000 on the secondary. What is the output if the input is 120v?
A transformer has 1000 turns on the primary side and 2000 on the secondary. What is the output if the input is 120v?
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If the conductor in an AC circuit is wound into a coil, the resulting EMF opposes supply voltage. This is called:
If the conductor in an AC circuit is wound into a coil, the resulting EMF opposes supply voltage. This is called:
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To change rotation on a 3-phase motor:
To change rotation on a 3-phase motor:
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A solenoid valve operates on the principle of:
A solenoid valve operates on the principle of:
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A ___ is commonly used on a single phase fractional horsepower compressor to disconnect the start winding.
A ___ is commonly used on a single phase fractional horsepower compressor to disconnect the start winding.
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The rotation of a single phase motor is determined by:
The rotation of a single phase motor is determined by:
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Single phase motor speed is determined by:
Single phase motor speed is determined by:
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Capacitor-start, capacitor-run motors provide:
Capacitor-start, capacitor-run motors provide:
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Direct digital control (DDC) is:
Direct digital control (DDC) is:
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What connects the T1, T2 and T3 terminals on a contactor?
What connects the T1, T2 and T3 terminals on a contactor?
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A step-up transformer increases
A step-up transformer increases
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Utility companies usually provide residential homes with:
Utility companies usually provide residential homes with:
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Transformers are rated by:
Transformers are rated by:
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Circuit breakers and fuses are used to provide:
Circuit breakers and fuses are used to provide:
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Excessive current can be caused by:
Excessive current can be caused by:
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A device with overload protection used to control a motor is a:
A device with overload protection used to control a motor is a:
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What is the minimum number of wires required between two start/stop push button controls?
What is the minimum number of wires required between two start/stop push button controls?
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If contacts become badly pitted, it is acceptable to:
If contacts become badly pitted, it is acceptable to:
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The thermal overload contacts on a line starter are usually ___ reset.
The thermal overload contacts on a line starter are usually ___ reset.
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Which of the following motors is most energy efficient?
Which of the following motors is most energy efficient?
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Contactors are rated according to the maximum amperage through the:
Contactors are rated according to the maximum amperage through the:
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The ____ drawing illustrates where the components are located on the appliance.
The ____ drawing illustrates where the components are located on the appliance.
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On a good single phase compressor, which winding terminals have the highest resistance?
On a good single phase compressor, which winding terminals have the highest resistance?
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When testing a motor with an ohmmeter, the following measurements are recorded; C to R = 4, C to S = 6.2, R to S = 10.2, R to ground = 20.4. This indicates:
When testing a motor with an ohmmeter, the following measurements are recorded; C to R = 4, C to S = 6.2, R to S = 10.2, R to ground = 20.4. This indicates:
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With a motor running at full load, voltmeter leads are placed on L1 and T1 with no measurable voltage detected. This indicates:
With a motor running at full load, voltmeter leads are placed on L1 and T1 with no measurable voltage detected. This indicates:
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When the temperature of a negative temperature coefficient (NTC) thermistor increases, its resistance:
When the temperature of a negative temperature coefficient (NTC) thermistor increases, its resistance:
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When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance:
When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance:
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The most common type of transducer used with HVAC/R equipment creates a signal based on:
The most common type of transducer used with HVAC/R equipment creates a signal based on:
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A thermocouple can:
A thermocouple can:
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To discharge a capacitor:
To discharge a capacitor:
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Which of the following is an acceptable temporary replacement capacitor for a 35MFD, 440VAC capacitor?
Which of the following is an acceptable temporary replacement capacitor for a 35MFD, 440VAC capacitor?
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When checking the windings on a three phase motor, the resistance readings should:
When checking the windings on a three phase motor, the resistance readings should:
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Capacitors are always connected _____ with the start winding?
Capacitors are always connected _____ with the start winding?
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The symbol for a heating thermostat is represented by:
The symbol for a heating thermostat is represented by:
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The symbol for a pressure switch that closes on a rise of pressure is represented by:
The symbol for a pressure switch that closes on a rise of pressure is represented by:
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The symbol for a pressure switch that opens on a rise in pressure is represented by:
The symbol for a pressure switch that opens on a rise in pressure is represented by:
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The synchronous speed of a four pole, 60 Hz single-phase motor is:
The synchronous speed of a four pole, 60 Hz single-phase motor is:
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The symbol for a transformer is:
The symbol for a transformer is:
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The symbol for a thermal overload is:
The symbol for a thermal overload is:
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The symbol for a pressure switch is
The symbol for a pressure switch is
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The symbol for a thermostatic switch is:
The symbol for a thermostatic switch is:
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In the schematic, what voltage would be found across L1 to L2?
In the schematic, what voltage would be found across L1 to L2?
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In the schematic (during operation) what voltage would be found across the condenser fan motor?
In the schematic (during operation) what voltage would be found across the condenser fan motor?
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In the schematic (during operation) what voltage would be found across the transformer primary?
In the schematic (during operation) what voltage would be found across the transformer primary?
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In the schematic, what voltage would be found from terminal G to the load side of the transformer? (Assume the thermostat is in the closed position and the fan is set to auto.)
In the schematic, what voltage would be found from terminal G to the load side of the transformer? (Assume the thermostat is in the closed position and the fan is set to auto.)
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In the schematic, what voltage would be found (during operation) across the contacts when energized in line #8? (Assume the thermostat is in the closed position and the fan is set to auto.)
In the schematic, what voltage would be found (during operation) across the contacts when energized in line #8? (Assume the thermostat is in the closed position and the fan is set to auto.)
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In the schematic, what voltage would be found from terminal Y to the input side of the coil on line #11? (Assume the thermostat is in the closed position and the fan is set to auto.)
In the schematic, what voltage would be found from terminal Y to the input side of the coil on line #11? (Assume the thermostat is in the closed position and the fan is set to auto.)
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When troubleshooting an A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and the condenser fan motor are short cycling. The blower motor is not running. This could be caused by?
When troubleshooting an A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and the condenser fan motor are short cycling. The blower motor is not running. This could be caused by?
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When troubleshooting an A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and the condenser fan motor are not running. The blower motor is running. This could be caused by?
When troubleshooting an A/C system in the schematic, the following conditions are found. The thermostat contacts are closed. The compressor and the condenser fan motor are not running. The blower motor is running. This could be caused by?
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In the schematic, a faulty thermostat - auto / fan on switch means?
In the schematic, a faulty thermostat - auto / fan on switch means?
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In the schematic, the crankcase heater will operate;
In the schematic, the crankcase heater will operate;
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In the schematic, the coil on line #11 does not control;
In the schematic, the coil on line #11 does not control;
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Study Notes
Electrical Basics
- Current flow is the movement of electrons in a circuit.
- Impedance is the opposition to alternating current (AC).
- Like charges repel each other, while unlike charges attract.
- A conductor is a material that easily releases electrons.
- Current is represented by the symbol "I".
- Electricity can produce light, heat, and magnetism.
Electrical Components and Conductors
- Safety ground conductors are typically colored green.
- Electrons have a negative charge.
- Silicon is considered the best material for use as a semiconductor.
- An ohmmeter must use internal power to check a load or circuit.
- A typical 24 volt, 20 ohm contactor coil in series with a 200 ohm control relay will only activate the control relay.
Circuit Calculations
- In a parallel circuit with three 15 ohm defrost heaters connected to 120 volts, total power consumed is 2880 Watts.
- Resistance needed in a 120 volt circuit to limit current to 2 amps is 60 ohms.
- Resistance is defined as opposition to electron flow.
- In electrical wiring, black wires indicate a hot conductor.
Power and Energy
- A heater drawing 5 amps on 460 volts consumes 2300 Watts.
- When connected in parallel, resistors maintain the same voltage drop across each as the source voltage.
- Three resistors in parallel (R1 = 30 ohms, R2 = 15 ohms, R3 = 10 ohms) result in a total resistance of 6 ohms.
- Watts can be calculated using the formula W = E × I.
Capacitors and Circuit Parameters
- Capacitors are grounded in series with the start winding of motors.
- Output voltage from transformers is dependent on primary and secondary turns; for instance, a transformer with 1000 turns on the primary and 500 on the secondary gives 60 volts output from 120 volts input.
- Transformers increase voltage; they are rated in volt-amperes (VA) at the secondary.
- A diode controls the direction of electron flow.
Motors and Control Devices
- An electronically commutated motor (ECM) is designed to provide optimal airflow under varying conditions.
- A solenoid valve operates on the principle of electromagnetism.
- Motors are rated according to the maximum amperage they handle.
- Thermal overload contacts in line starters are generally manually reset.
Troubleshooting and Tests
- When diagnosing a malfunctioning A/C system, symptoms include short cycling of compressors and fans which may indicate issues with a faulty blower motor or relay.
- A faulty thermostat may result in the inability to control fan operation correctly.
- Understanding that a crankcase heater operates when the compressor is off is crucial in troubleshooting.
- It is essential to discharge capacitors safely before testing with an ohmmeter.
General Electrical Principles
- Three-phase loads require a minimum of three supply lines.
- The correct wiring of electrical circuits is critical to prevent overloads and ensure safety.
- The synchronous speed of a four-pole, 60 Hz motor is approximately 1800 RPM, determined by the number of stator poles.
- The cancellation of magnetic fields in a two-wire circuit leads to zero ammeter readings.
Diagrams and Schematic Interpretation
- Schematic diagrams outline voltage readings at various points, critical for troubleshooting.
- The voltage across certain components can provide insights into equipment functionality and potential faults.
Capacitor Specifications
- Capacitors have specific ratings for microfarads (MFD) and voltage; acceptable temporary replacements adhere to these specifications.
- Capacitor analyzers check the capacitance of capacitors, determining their operational capability.
Circuit Safety
- Circuit breakers and fuses act as shields against excessive current, preventing overload situations.
- Understanding circuit symbols and schematic representations is crucial for recognizing components and their connections in electrical systems.
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