Advanced Electrical Troubleshooting: Chapter 1
Content
Motor Inspections Part 1
In this module, we will look at advanced motors and how to inspect them. There are single-phase motors and three-phase motors. Skip to quiz!
Single-Phase Motors
Recall that electric current is the flow of electrons. The term phase when talking about electricity refers to electrical current.
Recall that there are two types of current: AC and DC. DC circuits use a constant value of current, and AC circuits use waves of current.
“Phase” comes from studying the sine wave. Current flows in a sine wave in an Alternating Current (AC) circuit. The sine wave phase is the distance between its actual starting point shown in blue and the ideal starting point shown in red in the image.
Recall that motors are devices that turn electrical energy into mechanical energy. This means that they use electricity from your outlet and rotate their load. This load can be a wheel or a fan.
A single-phase motor uses a single current source. Single-phase motors have very simple setups. These single-phase motors are usually found in small home devices like fans, heaters, and refrigerators.
One kind of single-phase motor is a single-phase induction motor. It has two parts: the stator, which does not move, and the rotor, which moves. The power goes into the stator, and the load is connected to the rotor. A load can be a wheel that the motor is turning.
How to Inspect a Single-Phase Motor
Now that we know what a single-phase motor is, let's look at how to inspect it. The first step when testing a motor is to make sure the power supply is off.
Next, we want to check for any obvious signs of damage on the outside. Look for any burnt, dented, or other damaged areas on the body, fan, and shaft.
Next, we should rotate the shaft ourselves to see if it turns smoothly. If it is smooth, the motor is probably in good condition.
The following steps will test the electrical health of the motor. We are checking:
Earth Resistance,
Power Supply, and
Motor Capacitor
Let’s check the earth resistance of the motor. Recall that resistance is a property of circuit components that resists the flow of current.
The earth resistance is the “natural” resistance of the motor. We can measure this resistance using a multimeter.
Make sure the multimeter dial is set to Ω or “continuity” settings. Connect the probes to the earth wire and motor frame. If the multimeter shows 0.5Ω or less, the motor is fine. Otherwise, the motor is faulty.
Next is checking the power supply to the motor. The power supply is usually the outlet or battery pack that the motor is connected to.
Set the multimeter dial to V setting. Connect the probes to the +/- ports of the motor. If the multimeter shows 230V or more, the power supply is fine. Otherwise, the supply is faulty.
The last test is to check the capacitor. Recall that a capacitor is an electrical component that stores energy. It will help get the motor started.
Set the multimeter dial to C setting. Connect the probes to the +/- sides of the capacitor.
There will be a written number for the expected value of a capacitor with a tolerance. Capacitance is often written as a value +/- the tolerance on the body of the capacitor.
If the multimeter reads outside the tolerance, then the capacitor is likely faulty. For example, if a capacitor were made as 100 μF +/- 10%, we would expect the actual tolerance to be between 90 to 110 uF.
Three-Phase Motors
While single-phase motors are suitable for many small devices, commercial and industrial devices need much more power to run.
A three-phase motor uses three current supplies. Instead of a single sine wave, we now have three sine waves, and all spread out to reach peak current at three times the single rate.
Three-phase motors also have a stator and a rotor, just like single-phase. The stator does not move and accepts the electrical power. The rotor is attached to the rotating load.
Three-phase motors offer a lot of advantages:
They can run much larger loads for industrial uses.
They do not require any motor starters, unlike single-phase.
They operate at the peak current 3 times per cycle instead of 1
There are some disadvantages, however. First, because the power supply is so large, there is a high cost of wire insulation. Recall that insulation is a method of protecting wires from unwanted electrical contact, such as a human touch or to another metal component.
Three-phase motors cannot handle overload. As a result, when the motor is damaged, it is difficult and expensive to fix. This is because having three power sources makes taking the motor apart and identifying the faulty components difficult.
How to Inspect a Three-Phase Motor
Inspecting a three-phase motor starts the same way as a single-phase motor. Start by making sure the power supply is off. Next, we want to check for any obvious signs of damage on the outside. Look for any burnt, dented, or other damaged areas on the body, fan, and shaft.
The next test is to check the earth resistance of the motor. Recall that the earth resistance is the “natural” resistance of the motor.
Set the multimeter dial to Ω or “continuity” settings. Connect the probes to the earth wire and motor frame. If the multimeter shows 0.5Ω or less, the motor is fine. Otherwise, the motor is faulty.
The last step is to check the motor’s winding resistance. We will explain this process in the next topics.
Motor Inspections Part 2
In this module, we will look at more advanced motor components and how to inspect them. The motor components are motor windings and motor starters. Skip to quiz!
Motor Windings
Motor windings are rings of conductive wire in the motor. They are usually wound around a metal object, or “core.”
The wires are insulated from the outside and also insulated from each other. This forces the current to travel the intended path and not skip across wires.
Recall that when current flows through the loop, it creates a magnetic field that makes the motor turn. Usually, the more turns there are, the stronger the magnetic field is, which makes a stronger motor.
In the motors we have talked about, there is one winding for each stator and rotor. The stator windings accept the 3-phase AC supply. The rotor winding accepts the Direct Current (DC) supply. Recall that DC is a constant value, not a wave.
As with any component, motor windings can also fail. The coils of different phases (like in the three-phase motors) need to be separated from each other to avoid damage.
How to Inspect Motor Windings
When inspecting the motor windings, we are just checking the motor resistance. We will use a multimeter to do this. The multimeter needs to be connected to the motor terminals, so we must remove the motor casing to find them.
Set the multimeter dial to the highest Ω settings. Connect the multimeter probes to both ends of each winding. If the multimeter shows a value of resistance, the winding is working.
If there is an “OL,” there is likely a break in the wire. “OL” stands for “Open Loop.” An open loop does not have continuity across the wire. If a wire is broken, the motor windings would need to be replaced.
It is also possible for the windings to short-circuit. A short circuit is when there is accidental contact in the circuit, which can cause the circuit to overheat and fail. If there is a short circuit in our motor, it would be because a winding is touching the conductive motor frame.
To check, attach a multimeter probe to a winding and the other probe on the motor frame. If there is a resistance value, the winding has caused a short circuit. If it reads “OL,” then the current is staying in the wire. That means there is no short circuit.
Motor Starters
Single-phase and some three-phase motors need additional help to start running. One current supply does not give enough power to start up, so we must add another device called a motor starter to the circuit.
Motor starters are electrical devices that help a motor start and stop safely. It also protects the motor.
The main functions of motor starters are:
To safely start a motor
To safely stop a motor
To change the direction of a motor (clockwise to counterclockwise)
To protect the motor from overload
For a three-phase motor, a motor starter is needed to limit the starting current. Having too high of a current can cause overheating and damage. Therefore, the motor starter will only function at startup, and then the normal current and voltage will run the motor.
How to Inspect a Motor Starter
We can inspect the motor starter using a multimeter. Set the multimeter dial to the continuity setting. Make sure the motor and starter are off. Calibrate the multimeter by touching the two wires together until it reads close to zero.
Recall that motor starters may have multiple terminals. Two of them are coil terminals. And four to six terminals of these input-output terminals.
First, we need to check the coil of the motor starter. Attach the probes to the coil terminals. The multimeter should read a resistance value. If the multimeter reads “OL,” the circuit is broken, and the motor starter is faulty.
Next, we need to check the motor starter contacts. Attach the multimeter probes to the input (L1) and output (T1) terminals. It should read “OL” or “1”. If it shows resistance, then the motor starter is faulty. It is faulty because the motor starter is closed in the ON state, which is incorrect.
Lastly, we need to repeat the previous steps after closing the starter contacts. This means that the motor starter would be activated and should form a complete circuit. If there is resistance, then the motor starter is working correctly. Otherwise, if it shows “OL” or “1”, the starter is faulty.
Motor windings are conductive wires inside the motor. They use current to create a magnetic field. Running motor windings in good condition will always show a resistance value. It will always show “OL” for a short circuit.
Motor starters are devices that help motors start running. They also protect the motor from damage.
Electrical Inspections - Signal Lights
In this module, we will talk about signal lights. By the end of this module, you will be able to inspect signal lights. Skip to quiz!
Signal Lights
In HVAC systems, the control boards are installed with signal lights to indicate the service status. Recall that control boards are the brains of an HVAC unit that receive inputs and give out signals to perform different activities. The signal lights display a failure code which helps the technician to identify the faults.
Different colors of signal lights present in the furnace control board represent different functions. These signal lights are commonly red, green, and yellow.
How to Inspect Signal Lights
Recall that signal lights refer to specific problems in an HVAC unit. The function of signal lights can be summarized here:
A slow flash on the red signal light indicates normal operation.
A quick flash indicates normal operation and calls for heat.
Two blinks indicate a flame switch failure.
A three blink on the signal light indicates a pressure switch failure.
The four blinks indicates a faulty temperature switch.
The continuous blinks on the signal light indicates a failed controller.
No signal light in the control board indicates no power to the furnace.
In this module, you learned about signal lights. Signal lights indicate the service status in an HVAC system.
In this module, you learned how to inspect signal lights. The number of blinks in the signal lights correspond to different error signal in an HVAC system.
Electrical Inspections - Capacitors
In this module, we will look at a common motor circuit component - capacitors. By the end of this module, you will be able to understand how a capacitor works and how to troubleshoot a capacitor. Skip to quiz!
Capacitors
Recall that a capacitor is a device that stores electrical energy. It stores energy in the form of an electric field that is created between two charged plates.
Two conductive metal plates are physically separated either by air or an insulating material like paper or plastic. This allows for each plate to store electric charge. If the plates were touching, then the capacitor would be no different from a wire.
Capacitance is related to the area and distance between the plates. Capacitance is directly related to plate area and inversely related to the separation distance. This means the bigger the plates are and the closer they are together, the higher the capacitance.
There are three common types of capacitors. Single run capacitors have two terminals. Dual run capacitors have three terminals. Start capacitors have two terminals and are often used for the startup.
Capacitors are designed for many different types of systems. Some systems, like strong motors, need much higher capacitance ratings than others, like small electronics. Capacitor ratings are usually printed on the body and are measured in Farads (F).
In a single-phase motor, the capacitor’s functions are:
Set the rotation direction - clockwise or counterclockwise,
Provide power needed to start the motor, and
Increase power while the motor is running.
How to Inspect Capacitors
The capacitance is the most important quantity to check if a capacitor is working correctly. We will use a multimeter on the capacitance (C) setting to test it.
First, we disconnect the capacitor from the circuit. We need to discharge the capacitor to get rid of any leftover charge inside. The safest way to discharge the capacitor is by connecting the terminals of the capacitor with a resistor.
We can also use a screwdriver or other conductive device. Make sure your alternate device has an insulated handle like in the video. This will protect you from electric shock.
When the capacitor is disconnected and discharged, make sure there are no physical damages to the capacitor. Look for dents, dirt, burn marks, damaged terminals, or bulging.
The designed capacitor ratings (MFD) should be printed on the body. Make a note of the value and the tolerance. Recall that this capacitor is rated at 7.5μF with a tolerance of 5%. We would expect the measured value to be between 7.1-7.9 uF.
Recall that dual-run capacitors have three terminals - FAN, COMM, and HERM. They will show two ratings. The first, larger value is between the HERM and C terminals. The second, much smaller value is between the FAN and C terminals.
Dual run capacitors usually will only have one tolerance value. This tolerance applies to both ratings. Let’s look at an example of this 45/5uF capacitor with 6% tolerance.
This capacitor has a rating of 45 uF between the HERM and C terminals. Six percent of 45 is 2.7. We should expect a reading between 42.3 and 47.7 uF between HERM and C.
The capacitor also has a rating of 5 uF between the FAN and C terminals. Six percent of 5 is 0.3. We should expect a reading between 4.7 and 5.3 uF between FAN and C.
Place the black multimeter probe on the C terminal. Connect the red probe to one of the other terminals for a dual-run capacitor.
Compare the multimeter reading to the capacitor ratings. If they are within the specified tolerance, then the capacitor is functioning correctly.
If we are reading values very far from the expected values, then the capacitor is faulty.
In this module, you learned about capacitors in motor systems. Capacitors hold a charge to help motors start and change direction and protect motors from electrical damage.
You also learned the process of troubleshooting capacitors when the motor is not working correctly. We need to check if the capacitance across the terminals is within the specified tolerance. For dual-run, there are two values that need to be checked.
Electrical Inspections - Relays
In this module, we will look at another common motor circuit component: relays. By the end of this module, you will be able to define a relay, learn the construction of a relay and to know how to troubleshoot a relay. Skip to quiz!
Relays
Think of a basic light switch in your house. To get the lights to turn on, we have to manually flip the switch. Now, what if there was a way to have the lights turn on automatically when it gets dark out? For this, we could use an electrical relay.
Relays are switches that are operated by electrical signals. There are tons of different relays for a variety of uses and sizes. Relays are normally used in control panels, manufacturing, and building automation to control power sources.
Relays are used in high-powered loads instead of manual switches. Relays are also quicker to respond to. These loads include air conditioners, motors, street lights, and more. Switches are usually only used for low-power uses like house lights and fans.
Most relays have four main pins. Two will be the terminals on either side of the switch. The other two will be the terminals for the electrical signal that will open or close the switch.
The pins on relays will be numbered, and most relays have diagrams on the casing. For a four-pin relay:
Pin 30 will be upstream of the switch,
Pin 87 will be downstream of the switch, and
Pins 85 and 86 will be the signal terminals
The main purpose of a relay is to make or break contact in the circuit without human involvement. As seen in the video, when the armature is energized, it attracts the contact, completing the circuit. Relays generally use a DC signal for control.
The DC signal is driven by high voltage AC home appliances through microcontrollers. A microcontroller is a tiny computer chip that is programmable to help us control electrical systems.
How to Inspect Relays
First, we need to power off the circuit and control power, then disconnect the relay. We should check for any obvious external damage. Look for dents or burn marks on the casing of the relay.
As seen in the video, the relay has an open switch when no power is applied. We will need to check the relay both with and without control power.
Next, we’ll use a multimeter to check the terminals of the relay. Set the multimeter to the Ω or continuity setting. Use the highest setting if there are multiple.
For most relays, there will be 4 terminals. Three will be oriented the same way, and the fourth will be perpendicular.
The perpendicular terminal will be the “outlet” of the relay. The center of the remaining three will be the “inlet.” The other two are the control pins.
Start by measuring the resistance across the two control terminals. There should be a resistance value. If the multimeter reads very high resistance or “OL,” the relay is faulty. This means there is a break in the coil that would prevent the relay from working.
Now, test the inlet and outlet terminals. The multimeter now should read “OL.” This is because the switch should be open without any applied control voltage.
If the multimeter shows resistance across the hot terminals, then the switch is stuck in the closed position. This means the relay is faulty, as the switch should be open with no applied control voltage. Now we will look at how to inspect a relay with control power applied.
We need to test the relay when the switch is closed. Attach two wires to a low voltage power source, like a battery or a jumper box, as seen in the video. Attach the two wires to pins 85 and 86, the control coil terminals.
When the wires are connected, and the power source is on, we should hear the relay click. The click is the switch changing to the closed state, allowing the current to pass through the circuit. Detach one of the power source wires.
Now, set the multimeter to the continuity settings. Attach one multimeter probe to pin 30 and the other to pin 87. This will test continuity across the switch when it is closed.
Now, attach the wire that completes the control side. The multimeter should beep to show continuity. If it does not beep, there is no continuity. This means that the switch does not change to the closed state. The relay is then faulty.
In this module, we learned about electrical relays. Relays act as switches that activate electrical signals. We know how they work and how to use all terminals to set up a relay circuit properly.
We also learned how to troubleshoot a relay. With no control power, the control side should show resistance, and the circuit side should show “OL.” With control power, the circuit side should show continuity.
Question #1: Phase is a property of a:
Motor
Sine wave
Material
Technician
Scroll down for the answer...
Answer: Sine wave
Phase is seen in an AC circuit, which has a sine wave for current.
Question #2: Single-Phase motors have _____ current sources:
1
2
3
Scroll down for the answer...
Answer: 1
Single-phase motors have 1 current source. Remember, “phase” refers to alternating current.
Question #3: When checking for resistance, the multimeter should be set to:
V
Ω
C
A
Scroll down for the answer...
Answer: Ω
Resistance is measured in Ohms (Ω). The multimeter will measure resistance on this setting.
Question #4: Capacitors are labeled as:
Value
Value +/- tolerance
Tolerance +/- value
Capacitors are not labeled
Scroll down for the answer...
Answer: Value +/- tolerance
Remember that the value is what the part is designed for. However, tolerance needs to be included to account for slight changes part-to-part.
Question #5: The main areas of inspection for a single-phase motor are (select all that apply):
Capacitor
Earth Resistance
Power Supply
Weight
Scroll down for the answer...
Answer: Capacitor
Earth Resistance
Power Supply
For inspecting a single-phase motor, we always inspect the earth resistance, then the power supply, and then the capacitor.
Question #6: The stator ____ and the rotor _____ .
Moves, does not move
Moves, moves
Does not move, moves
Does not move, does not move
Scroll down for the answer...
Answer: Does not move, moves
The stator is stationary (does not move). The rotor rotates (moves).
Question #7: Three-phase motors have:
Three current sources
Three shafts
Three power supplies
Three stators
Scroll down for the answer...
Answer: Three current sources
Three-phase motors have three phases, or AC current sources.
Question #8: Three-phase motors are used for ________ and single-phase motors are used for _______ .
Small uses, small uses
Small uses, large uses
Large uses, small uses
Large uses, large uses
Scroll down for the answer...
Answer: Large uses, small uses
Single-phase motors are used for small home devices. Three-phase motors are used in industry.
Question #9: Motor windings are insulated (select all that apply):
From each other
From the outside
From the power supply
Scroll down for the answer...
Answer: From each other
From the outside
To avoid short circuits, motor winding wires are insulated from each other and any outside surfaces.
Question #10: The more windings there are in a motor, the:
Weaker the magnetic field
Stronger the magnetic field
Weaker the motor
Stronger the motor
Scroll down for the answer...
Answer: Stronger the magnetic field
Stronger the motor
With more windings, the magnetic field becomes stronger. This results in the motor being able to handle larger loads.
Question #11: When inspecting the windings, the multimeter reads 0.005 Ω. This means:
There is a short circuit
The wire is broken
The wire is functional
The motor is broken
Scroll down for the answer...
Answer: The wire is functional
If windings give a value for resistance, then they are functional. If they say “OL,” which means “Open Loop,” they are faulty.
Question #12: Motor starters (select all that apply):
Help the motor start
Act as the load
Protect the motor from overload
Function the entire time the motor is running
Scroll down for the answer...
Answer: Help the motor start
Protect the motor from overload
Motor starters help the motor start and protect it from overload. Motor starters only function at motor startup.
Question #13: Motor starters check should include:
Coils
Contacts
Both
Neither
Scroll down for the answer...
Answer: Both
When inspecting motor starters, we need to inspect both the coils and the contacts.
Question #14: Signal Lights are present in the HVAC systems, which indicates specific faults or errors.
True
False
Scroll down for the answer...
Answer: True
The low voltage signal lights present in the control board point towards different types of faults in the HVAC system.
Question #15: Two blinks with a pause in the signal light of a gas furnace indicate:
Failed temperature sensor
No power
Normal operation
Failed flame switch
Scroll down for the answer...
Answer: Failed flame switch
Two blinks with a pause in the signal light will indicate the flame switch in the gas furnace is not working or faulty.
Question #16: Which of the following would not be a good medium between capacitor plates?
Plastic
Paper
Aluminum
Air
Scroll down for the answer...
Answer: Aluminum
Capacitor plates need to be separated by non-conductive materials. Plastic, paper, and air are all non-conductive. Aluminum is very conductive.
Question #17: Capacitors store energy in the:
Electric Field
Magnetic Field
Wires
Motor
Scroll down for the answer...
Answer: Electric Field
Capacitors store energy in the electric field created between their charged plates.
Question #18: Which of the following combinations would provide the largest capacitance?
Large plates, large separation
Large plates, small separation
Small plates, large separation
Small plates, small separation
Scroll down for the answer...
Answer: Large plates, large separation
Recall that capacitance is directly related to surface area and inversely related to the separation distance. Therefore, a capacitor with large plates and a small separation distance will have the highest capacitance.
Question #19: A capacitor is rated at 100 uF with a tolerance of 10%. Which of the following readings shows a faulty capacitor?
100 uF
106 uF
94 uF
118 uF
Scroll down for the answer...
Answer: 118 uF
The thermostat is connected to a capillary tube which consists of gas.
Question #20: What can we use to discharge a capacitor? (select all that apply)
Resistor
Inductor
Screwdriver
Insulator
Scroll down for the answer...
Answer: Resistor
Screwdriver
The safest way to discharge a capacitor is by using a resistor. Other conductive devices with insulated handles, like a screwdriver, can also be used.
Question #21: We should consider replacing a capacitor if we see (select all that apply):
Rust
Dents
Burn marks
Bulging
Scroll down for the answer...
Answer: Rust
Dents
Burn marks
Bulging
Any visual damage to the capacitor is a reason to consider a replacement.
Question #22: Single run capacitors have ___ rating(s) and ___ tolerance(s).
One, one
Two, one
One, Two
Two, two
Scroll down for the answer...
Answer: One, one
Single run capacitors have only one rating between the two terminals.
Question #23: Dual run capacitors have ___ rating(s) and ___ tolerance(s).
One, one
Two, one
One, Two
Two, two
Scroll down for the answer...
Answer: Two, one
Dual run capacitors have two ratings (HERM-C, FAN-C). However, both ratings share the same tolerance.
Question #24: When inspecting a dual-run capacitor, the black multimeter probe should be attached to the ____ capacitor terminal.
HERM
FAN
C (COMM)
Scroll down for the answer...
Answer: C (COMM)
The black probe should be attached to the C (COMM) terminal. The red probe will be attached to the HERM or FAN for each reading.
Question #25: Relays are automated ______.
Capacitors
Batteries
Motors
Switches
Scroll down for the answer...
Answer: Switches
Relays act as automatic switches in circuits. They are activated by electrical signals.
Question #26: Switches use manual inputs, and relays use electrical signals to function.
True
False
Scroll down for the answer...
Answer: True
Relays are useful because they can be changed with electrical signals instead of physically activating the switch.
Question #27: Which of the following are terminals for the circuit’s current flow? (select all that apply)
30
85
86
87
Scroll down for the answer...
Answer: 30
87
Pin 30 is upstream, and pin 87 is downstream of the switch. This means that the current will flow into pin 30 and out of 87 in the circuit.
Question #28: Which of the following are terminals for the electrical switch signal? (select all that apply)
30
85
86
87
Scroll down for the answer...
Answer: 85
86
Pin 85 and 86 are used for activating the switch. When there is current between them, the coil will produce a magnetic field that closes the switch.
Question #29: The circuit side of the relay uses: (select all that apply)
Pin 30
Pin 85
Pin 86
Pin 87
Scroll down for the answer...
Answer: Pin 30
Pin 87
The circuit side of the relay uses pins 30 and 87. Pins 85 and 86 are on the control side.
Question #30: With no control power applied to the relay: (select all that apply)
The control side should be continuous
The control side should not be continuous
The circuit side should be continuous
The circuit side should not be continuous
Scroll down for the answer...
Answer: The control side should be continuous
The circuit side should not be continuous
With no control power, the switch will be open. The circuit side should be an open loop. The control side should always be continuous.
Question #31: With control power applied to the relay: (select all that apply)
The control side should be continuous
The control side should not be continuous
The circuit side should be continuous
The circuit side should not be continuous
Scroll down for the answer...
Answer: The control side should be continuous
The circuit side should be continuous
With control power, the switch will be closed. The circuit side should be continuous. The control side should always be continuous.