Electrical troubleshooting and schematic reading are two of the most important parts of an HVAC service technician’s job. If you have a thorough understanding of electricity, HVAC components, and schematics it will save you hours of time and heartache. If you do not, this  can be one of the most difficult, frustrating, and confusing parts of your job. There is nothing worse than misdiagnosing a component problem, telling the homeowner, replacing the part, only to find out that you misdiagnosed the problem.

There are three primary tools an HVAC technician uses to electrically troubleshoot an HVAC system, they are:

  • Voltmeter
  • Ammeter
  • Ohmmeter

Let’s first discuss the voltmeter. A voltmeter measures the difference in potential or the difference in voltage. For example if you put one lead of your voltmeter on a point that has 120 volts and the other lead on the same point. What would the voltmeter read?  120 volts – 120 volts = 0 volts. Now if you put one lead on 120 volts and the other lead on 0 volts, the reading would be 120 volts – 0 volts = 120 volts.

Knowing this, one way to troubleshoot an air conditioning control circuit is the hopscotch method. Using your schematic, you can identify the parts in the control circuit that may be defective. You then determine if these components are passing the voltage through them by measuring the voltage across their terminals. You start at one end of the control circuit and hopscotch or jump from one component to another until you find the component that has failed.

Then it requires more troubleshooting to determine if the component is bad or, is it a protection component that has shut down the HVAC system due to high temperatures, or refrigeration pressure problems.

There is much more to electrical troubleshooting than can be covered in one article, but this will give you a small piece of the troubleshooting puzzle.

Our HVAC Technician course has interactive voltage measurement exercises, online and on the schematic itself! This helps you learn and visualize how schematics are used to troubleshoot HVAC electrical problems. Please watch our HVAC training calender for our free HVAC training to see how the interactive exercise are used.

by Ron Walker

Ron Walker
Ron Walker

After retiring from the U.S. Marines and achieving his B.S. degree, Ron Walker entered the HVAC field. He has been an HVAC technician, service manager, and business owner. Working as a service manager, he spent many years training HVAC technicians to be more technically competent and really understand their trade. His passion for teaching and helping others resulted in the creation of HVAC Training Solutions, LLC.