• SkillCat Team

Electrical Troubleshooting: A Complete Guide

Updated: Jun 29

Intro to Electrical Troubleshooting : Chapter 1


Finding the Problem


In this module, we will introduce you to electrical troubleshooting. We will cover:

- What electrical troubleshooting is,

- Wiring diagrams, and

- The hopscotch method Skip to quiz!


Overview


All modern systems from HVAC systems to dishwashers eventually break down.

Troubleshooting is the process of:

  • Finding the problem within a broken system, and

  • Fixing the problem

You can troubleshoot any type of electrical equipment. Most jobs in the skilled trades involve troubleshooting. For example, an appliance technician may troubleshoot a broken dishwasher.

Troubleshooting allows us to fix equipment that is no longer working. For example, imagine that your new dishwasher stops working. Instead of replacing the dishwasher, you can troubleshoot the problem.


In general, equipment breaks down because one part is malfunctioning. All of the other parts in the system work as expected. Troubleshooting allows us to replace the bad component instead of the entire system.


Wiring Diagrams

Recall that a wiring diagram is a blueprint of the electrical components in a system. Wiring diagrams can tell you:

  • What components are in a system,

  • How components are wired, and

  • The flow of current in a system.

To troubleshoot a system, we often need to refer to a wiring diagram. The information on a wiring diagram helps us understand the components, wiring, and the flow of current. Without a wiring diagram, it is very difficult to start troubleshooting.

Recall that a wiring diagram has a line and a control side. The line side of the circuit is usually powered by 240V. The control side of the circuit is usually powered by 24V.


When troubleshooting, it can be helpful to break the line side of the circuit into the:

  • Line side, and

  • Load side

On the line side of the circuit, you will find switches like contactor switches. On the load side of the circuit, you will find electrical loads like motors.


The control side of a circuit has relays, safeties, and coils. For example, the thermostat on an HVAC system is usually found on the control side of the circuit. The control side of the circuit receives a lower voltage, for example 24V.


When we troubleshoot a system, a problem on the line or control side presents different problems. For example, a problem on the control side could be causing the thermostat to not call for heating or cooling. On the line side, a fan may not be running due to a bad winding.


The Hopscotch Method


Once we have read the wiring diagram, we can begin to troubleshoot the system. The hopscotch method is the most common method used to diagnose electrical problems.

The first step in troubleshooting is to find the source of the problem. The hopscotch method is a great way to find the component that is malfunctioning.


With the hopscotch method, you follow the flow of electricity in a circuit. At each component, you will take a voltage measurement with your multimeter. Recall that as voltage passes through a component, you will see a voltage drop.


You will measure the voltage across each component until you find a component that receives 0V. If a component has 0V, the specific component may be faulty.


Once we find a faulty component, we can use other tools to determine the specific problem. The hopscotch method helps us find the specific component that is faulty. Without the hopscotch method, we would have to test many more components to find the fault.


Troubleshooting Mindset


When troubleshooting, there is not a set order that you should follow when diagnosing a problem. The order of steps will change depending on the problem in the system. Solving unique and challenging problems is what makes troubleshooting interesting.

Even though there is no set process, it is important is to have a step by step method to find the problem.


Not using a step-by-step process to troubleshoot can:

  • Take a very long time,

  • Cause you to miss a problem, and

  • Lead to diagnosing the wrong problem

The hopscotch method is an example of a step-by-step process to find the problem in a system.


When you begin troubleshooting, always refer to the wiring diagram. Break the system down into the line, load, and control sides of the circuit. Once you have broken the system into components, you can systematically check each system.


In general, we recommend that you start on the control side of the circuit. For example, if you are troubleshooting an HVAC system, start by changing the thermostat value. If the unit turns on, then you know the thermostat is calling to the line side.


Once you know the problem is not in the control side, you can begin to check the line side of the circuit. In general, it is best to follow the flow of current through the system. A ladder diagram can help you visualize the flow of current in a system.


Following the current ensures that you do not miss a problem or identify a problem in the wrong component. For example, you are troubleshooting an HVAC system. A switch is malfunctioning. Any components after the switch will display a 0V measurement.


If you follow the flow of current, you will find that the switch is the main problem. If you do not follow the flow of current, any component you measure after the switch will display 0V. Replacing the component will not solve the problem since the switch is what needs to be fixed.


Replacing the wrong component is the main cause of callbacks in the skilled trades. Following the flow of current and using the hopscotch method will significantly reduce the chance of replacing the wrong component.


Once you find a problem, never assume that you are done troubleshooting. When you are troubleshooting, the main goal is to find the root cause of the problem. One major problem can make several smaller problems in the system.


If you stop troubleshooting without finding the root cause, the system will break again. For example, you find a blown fuse on a unit. Instead of just replacing a fuse, you need to ask why the fuse was blown. If you do not find what caused the fuse to blow, the system may break again.


In this module, you learned about the basics of troubleshooting.The hopscotch method is the most common method of diagnosing problems in an electrical system. It is important to follow the flow of current in a methodical and step by step process when troubleshooting.




Diagnosing the Problem


In this module, we cover types of electrical faults including:

- Open circuits,

- Overamping, and

- Short circuits

We will also review grounding. Skip to quiz!


Electrical Faults


If a component is not working, we say that the component has a fault. An electrical fault is the specific reason that a component is not working.

Recall that the hopscotch method is used to find components with a 0V reading. With the hopscotch method, we can identify the damaged components within an electrical system. Knowing that a component has 0V flowing through it is not accurate enough for troubleshooting.


We need to identify the specific reason that the component is not working. If we do not determine the specific fault, the repairs we make may be unnecessary, or they may not work.


For example, a motor you are inspecting is not working properly. This alone is not enough to replace the motor. The motor could have a bad capacitor or a shorted winding. Depending on the problem, we would use a different repair.


Types of Electrical Faults


There are several types of electrical faults including:

  • Open circuits,

  • Overamping, and

  • Short circuits

We will explain each type in the coming slides.


Open Circuits


One common type of fault is an open circuit. An open circuit refers to a system that does not have complete path for current to flow. An open circuit is usually caused by a broken wire.

Note that the switch is in an open position. This is an open circuit since there is no path for current to flow.


Several items can cause an open circuit including:

  • A broken wire,

  • Lack of power, and

  • An open switch


To check for an open circuit, we will use the continuity setting on your multimeter. Start by setting your multimeter to continuity.


Insert the black connector into the COM port. The red port should be inserted into the mVΩ port. Touch the tip of your leads together.You should hear a beep sound and the display should say 0.


To find the open circuit, you want to check each part of the component. For example, the indoor fan motor on an HVAC unit is not running.You would need to check the wiring, windings, fan relay, and other components for continuity.


To measure continuity, press your leads on opposite terminals of the part. Place one lead on the terminal entering the component. Place the other lead on the terminal exiting the component.


If the meter beeps and displays a value close to 0, there is continuity.If it is an open circuit, your meter will display “OL”. Continue checking parts until you find the open circuit.


For example, you are checking the continuity of a light switch. Your meter displays a value close to 0. In this case, 0.01. Since the meter displayed a value close to 0, there is continuity across the switch. This means the switch is in the closed position.


Overamping


Another common electrical fault is overamping. All electrical equipment is designed to work safely under a certain amount of current. A component is overamping if it receives current above the safe limit.

If a component receives too much current, the component can be damaged. The current limit for a component can be found in the data sheet. Recall that the data sheet contains information on the part. It is created by the manufacturer.


To determine if a component is overamping, start by checking the data sheet. The data sheet will tell you the maximum current that the component is rated to handle.


To determine if a component is overamping, we will use a clamp multimeter. Recall that a clamp multimeter has a claw on top. The claw can measure the current of a wire inside the claw.


Start by grabbing your clamp multimeter. Open the jaws of the clamp meter. Close the jaws of the multimeter so that the wire is in the middle of the clamp.


If your meter displays a higher current than the data sheet, then the component is overamping. If a component is receiving too much current, it will heat up and be destroyed.


If a component is overamping, it will usually be damaged when you see it. For example, a blown fuse indicates that the system had too much current. You should look for the reason the system has too much current. Do not just replace the fuse.


Short Circuits


A short circuit is another type of electrical fault. A short circuit refers to a system that has an unintended and low resistance path for current to flow. The low resistance draws large amounts of current which can damage the system.

In the field, there is a common misunderstanding that a short circuit describes all broken components. A short circuit is a specific type of electrical fault.


Just like an open circuit, we will measure continuity to find a short circuit. We will measure the continuity from the hot wire to ground. Recall that to check an open circuit, we measured from the entrance to the exit of the component.


Start by setting your multimeter to continuity. Insert the black connector into the COM port. The red connector should be inserted into the mVΩ port.Touch the tip of your leads together. You should hear a beep sound and the display should say 0.


Place one lead on the hot terminal of the component. The other lead should be placed on the ground terminal.


If the meter displays OL then there is not a short circuit in that specific section. You can then check the next part for a short circuit. If the meter display a value close to 0, there is a short circuit in the part.


Ground Faults


Recall that grounding refers to connecting electrical systems to the earth.

There are two types of grounding:

  • Equipment grounding, and

  • System grounding

Equipment grounding connects components to non current carrying conductors. For example, an equipment ground may connect a component to a conduit or junction box.

System grounding connects the neutral points of a conductor to the earth. For example, a system ground may connect a transformer to the earth. In general, system grounds are poles driven deep into the earth. You can see them highlighted in the image.


In general, grounding is designed to keep you safe when touching electrical equipment. If a component is not grounded, you can be shocked when touching it.


When you are troubleshooting, always make sure that the system is grounded.If you work on an ungrounded system, you can be shocked.


In this module, you learned about common types of electrical faults. Finding the specific type of electrical fault allows us to effectively repair the component.


We covered several types of electrical faults including:

  • Open circuits

  • Overamping, and

  • Short circuits

We also gave an overview of grounding. Be extremely careful if a components ground is damaged.




Testing Capacitors & Motors


In this module, we will cover how to inspect:

- A single run capacitor,

- A dual run capacitor, and

- A seized motor Skip to quiz!


Capacitor Overview


Recall that an electrical fault is a system failure that prevents a component from running. A bad capacitor is one of the most common electrical faults.

Recall that a capacitor is a device used to store electrical energy in a circuit. The next few slides will teach you how to check if a capacitor is running correctly.


A faulty capacitor will not store electrical energy. To test if a capacitor is faulty, we will use the farads setting on our multimeter. Recall that farads is the unit of measurement for capacitance.


Before handling a capacitor, we need to disconnect the capacitor from the system. Remove the wires from the terminals of the capacitor. Pull the capacitor out of the system.


To test a capacitor, we need to discharge it. Recall that capacitors can store electrical energy even after the power to the circuit has been turned off.To discharge a capacitor, place a test resistor across the two terminals of the capacitor.


Next, we need to set up our multimeter. Turn the multimeter dial to the farads setting. The black connector plugs into the COM port. The red connector plugs into the port with the capacitance symbol.


Recall that there are two types of capacitors:

  • Single run capacitors, and

  • Dual run capacitors

A single run capacitor will have two terminals. A dual run capacitor will have three terminals.


Recall that both types of capacitors come with a capacitor rating. For example, it is common to see a capacitor rated for 7.5 microfarads. Recall the symbol for microfarads is µF. You can see an example of a capacitor rating in the image.


Single Run Capacitors


To measure the capacitance of a single run capacitor, we need to place one multimeter probe on each terminal.


If the measurement on your multimeter is within 10% of the capacitor’s rating, then the capacitor is functioning well. If the value is above or below the 10% range, then the capacitor needs to be replaced.


For example, you are measuring a 7.5µF single run capacitor. If your multimeter displays a value of 7.3µF, the capacitor is working correctly. If your multimeter displays a value of 3.4µF, the capacitor needs to be replaced.


Dual Run Capacitors


Recall that a dual run capacitor has three terminals. The terminals are labeled HERM, COM, and FAN. You can see a typical dual run capacitor in the image to the right.

Dual run capacitors have a different rating system than single run capacitors. A dual run capacitor may be labeled 45/5 microfarads. The first number (45) is the capacitance between HERM and COM. The second number (5) is the capacitance between FAN and COM.


For example, we are working on a 45/5µF capacitor. You would expect to see a 45µF rating when you connect your leads to the HERM and COM terminals. You would expect to see a 5µF rating when you connect your leads to the FAN and COM terminals.


Just like a single run capacitor, the capacitor needs to be replaced if the reading is above or below 10% of the rating. For example, if the reading is 30µF between HERM and COM then you need to replace the capacitor.


Before checking on a dual run capacitor, you need to short all three terminals. To short the capacitor, we will use a resistor. First place the resistor over COM and HERM. Then place the resistor over FAN and COM.


Once the capacitor is discharged, you need to measure the capacitance between the terminals. Start by placing your leads on HERM and COM. Then place your leads on COM and FAN. The black lead should always be on the COM terminal.


Be careful when replacing capacitors. A bad capacitor can be caused by another problem in the system. If you find a bad capacitor, check the rest of the system for potential errors. It is important to identify the root cause of any problems in a system.


Seized Motors


A common reason systems stop working is a problem with the motor. A seized motor is a common problem. A seized motor is a motor that is not working when it is receiving power.

Motors can fail for several reasons including:

  • A bad capacitor,

  • Shorted windings, and

  • Open windings


A seized motor will usually make a humming noise when the power is turned on. A humming noise from a motor generally means that the motor is seized.


Once you identify a motor is seized, there are a few things you can check. Most motors use a run capacitor to help start the motor. If a run capacitor has gone bad, the motor may not start.

You can also manually rotate the motor wheel. If the wheel feels sluggish, the motor is seized up.


In this module, you learned about electrical faults within capacitors. A bad capacitor is one of the most common causes of electrical failure. You also learned how to identify a seized motor.





Troubleshooting a System


This module will go through an example of troubleshooting an HVAC system. We will use the hopscotch method and our knowledge of common electrical faults to find the problem. Skip to quiz!


Overview

For this example, you are an HVAC technician. You have been called out to a customer’s home. The customer explains that the unit is not heating or cooling the house.


Recall that it is important to troubleshoot a system in a step by step process. A thorough process reduces the chance that you misdiagnose the problem.


In the wiring diagram to the right, you can see a ladder diagram of the indoor unit. We will refer to the ladder diagram to determine the flow of current through the system. You may also refer to a schematic diagram to view the wiring of components.


Finding the Problem


In this example, we want to start by confirming that the thermostat is working correctly. In other words, we are checking the control side of the system. We want to make sure that the thermostat is calling for heating or cooling.

To do this, go to the thermostat in the home. Set the thermostat to a value above or below the room temperature. This should cause the unit to turn on. Check the air vents to see if warm, cool, or no air is moving into the house.


In this example, there is no air coming out of the vents. This indicates a fault. We need to check what components are working in the indoor and outdoor units.


You may check if the following equipment is running:

  • Indoor fan motor,

  • Compressor, and

  • Condenser fan motor


If no equipment is running, the thermostat may not be calling for heating or cooling. If some equipment is running, the problem is most likely not in the thermostat.


In this example, you first check the outdoor unit. The compressor and compressor fan motor are both running. There does not seem to be a problem at the outdoor unit.


Next, we will check the indoor unit. You notice that the indoor fan motor is not running. This indicates that the problem may be associated with the indoor fan motor.


Reading the Diagram


We need to check what the possible causes are for the indoor fan motor not functioning. To check this, we will refer to the ladder diagram of the indoor unit.

After you read the indoor ladder diagram, you notice that several problems could have caused the indoor fan motor to not start.


Some causes could be:

  • A faulty fan switch in the thermostat,

  • The indoor fan relay is faulty,

  • A faulty run capacitor, and

  • A fault with the fan motor

Notice that each of these faults would stop current from flowing through the motor.


We need to troubleshoot each of these faults one by one. To test each component, we will use the hopscotch method. It is important that we check the components in the correct order. We must follow the flow of current or we may miss the problem.


Set your multimeter to measure AC voltage. Your black lead should be plugged in the COM port. Your red lead should be plugged into the mVΩ port.


Checking the Switch


Recall that there are several possible electrical faults including:

  • A faulty fan switch in the thermostat,

  • The indoor fan relay is faulty,

  • A faulty run capacitor, and

  • A fault with the fan motor

First, we need to check the fan switch in the thermostat.

To check the fan switch in the thermostat, we will confirm that the contactor coil of the relay is receiving 24V. When the fan switch is in the closed position, it allows 24V to pass to the contactor relay.


If the contactor coil receives 24V, then the fan switch in the thermostat is working correctly. If there is a 0V reading across the contactor coil, we know the problem is in the thermostat.


Place your leads on opposite ends of the relay contactor coil. Your meter reads 24V. This means that the fan switch in the thermostat is working. Next, we need to check if the relay is faulty.


Checking the Relay

To test the indoor fan relay, we start by checking the incoming voltage to the relay. Connect your multimeter leads to the terminals at the top of the relay. Your multimeter reads 240V. The indoor fan relay is receiving the correct amount of power.


Next, we will check if we have 240V on the load side of the relay. Place your leads on the outgoing terminals of the relay. The multimeter reads 240V. The problem is not with the indoor fan relay.




Checking the Capacitor


So far we have discovered the problem is not in the thermostat switch or the indoor fan relay. Next, we need to test the run capacitor.For this example, the dual run capacitor is rated 45/5µF.

Start by turning the power off and disconnecting the capacitor. Next, we need to discharge the capacitor. Place a 20KΩ, 5 W bleed resistor across the capacitor terminals.


Set your multimeter to measure capacitance. Place your black lead on the COM terminal of the capacitor. Your red lead should go on the FAN terminal. Your multimeter reads 4.9µF. The capacitor is working.


Next, you need to measure from HERM to COM. Place your black lead on the COM terminal of the capacitor. Your red lead should go on the HERM terminal. Your multimeter reads 44.2µF. The capacitor is working.


Checking the Motor


We have now checked ¾ of the possible problems. The last option is a fault with the fan motor. Remember that we have been following the flow of current through the system.

To check the motor, we need to try spinning the blower wheel. Recall that the blower wheel is supposed to smoothly spin. There also should not be a sound.


As you spin the blower wheel, you notice a sound and the wheel does not turn well. The sound and sluggish wheel tell us that the blower wheel may be obstructed. The cause of the no heat/no cool was a seized or faulty indoor fan motor.


In this module, we troubleshooted a residential HVAC system. It is important to use the hopscotch method to narrow down the potential problems. Once we know where the problem is, we can test each possible cause.





Question #1: The line side of a wiring diagram can include:

  1. Motors

  2. Evaporators

  3. Contactor switches

  4. All of the above

Scroll down for the answer...













Answer: All of the above

The line side of the circuit includes all components that are powered by 240V. This can include motors, evaporators, and contactor switches.


Question #2: The control side of the circuit will usually have:

  1. Coils

  2. Relays

  3. Safeties

  4. All of the above

Scroll down for the answer...












Answer: All of the above

The control side of the circuit will usually have the components powered by 24V. These components include coils, relays, and safeties.


Question #3: Following the flow of current means to:

  1. Check each component in the order it receives current

  2. Follow the water in the system

  3. Check each component in the reverse order it receives current

Scroll down for the answer...






Answer: Check each component in the order it receives current

Following the flow of current means to check each component in the order it receives current. This is critical to effectively using the hopscotch method.


Question #4: Once you fix the problem, you do not need to check the rest of the system.

  1. True

  2. False

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Answer: False

You must check the rest of the system after fixing the problem. Repairing the first problem could expose a second problem farther down the current flow.


Question #5: An open circuit is

  1. A very large circuit

  2. A circuit that does not have a complete path for current

  3. A circuit that does have a complete path for current

  4. A circuit with an unintended path

Scroll down for the answer...







Answer: A circuit that does not have a complete path for current

An open circuit does not have a complete path for current to flow. This can be caused by a broken wire, lack of power, or an open switch.


Question #6: To check for an open circuit, you

  1. Measure capacitance

  2. Measure continuity

  3. Touch the wire

  4. Replace the system

Scroll down for the answer...







Answer: Measure continuity

To check for an open circuit, you will measure the continuity of the part. It is important to place your leads at the entrance and exit of the part. For example, on a wire you will place one lead on each end of the wire.


Question #7: Overamping is:

  1. A component receiving too much current

  2. A component receiving too much voltage

  3. A component that does not have continuity

  4. A component that has too much capacitance

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Answer: A component receiving too much current

An overamping component is drawing too much current. This can damage the component if it is above the safe range.


Question #8: A short circuit is a common name for any type of problem in a component.

  1. True

  2. False

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Answer: False

A short circuit is a specific type of electrical fault in a unit. It is not a general term.


Question #9: There are two types of capacitors: single and dual run.

  1. True

  2. False

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Answer: True

There are two types of capacitors. Single run capacitors have two terminals. Dual run capacitors have three terminals.


Question #10: A capacitor is working as expected if it is within __% of the rating.

  1. 10

  2. 5

  3. 50

  4. 25

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Answer: 10

A capacitor is functioning well if it is within 10% of the rating. For example, a 10 microfarad capacitor is working with it is within 9-11 microfarads.


Question #11: A dual run capacitor with a rating of 45/5 microfarads would have:

  1. 45 microfarads between HERM and COM

  2. 5 microfarads between FAN and COM

  3. All of the above

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Answer: All of the above

A dual run capacitor would have a 45µF reading between HERM and COM. It would alsos have a 5µF reading between FAN and COM.


Question #12: A humming sound from a motor that is not running indicates that the motor may be seized.

  1. True

  2. False

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Answer: True

A humming sound from a motor that is not running indicates that the motor may be seized. You will need to check the capacitor and wheel to determine the cause.


Question #13: When troubleshooting it is important to:

  1. Follow the flow of current

  2. Use a step by step method

  3. Find the root cause of the problem

  4. All of the above

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Answer: All of the above

When you are troubleshooting you need to follow the flow of current and use a step by step method to avoid errors. It is also important to dive deeper into the problems you find and fix the root problem.


Question #14: The wiring diagram helps us determine the reasons a component may not be working properly

  1. True

  2. False

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Answer: True

A wiring diagram is critical to determining all the possible causes a component may not work.

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