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How to Use a Multimeter to Troubleshoot HVAC Problems.

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Problem: We have many people and potential customers who ask us to try and help troubleshoot their furnace and air conditioning systems without the use of a multimeter. In many cases, I suggest that people purchase a low-cost multimeter so they can find the problem. As we all know electricity, which is the flow of electrons in a conductor can not be seen so a multimeter is essential for troubleshooting HVAC systems. We sell multimeters on the following pages: the Fieldpiece SC260 Clamp Multimeter, The Ames Pocket-Sized Digital Multimeter Capacitor Tester, and UEi DL389B G2 Phoenix Pro Plus True-RMS AC Clamp Multimeter (With Temperature)

Solution: Purchase a good multimeter and learn how to use it. Below we have two really good YouTube videos on “How to Use a Multimeter”. The first video made by Word of Advice TV is very detailed and shows all the Multimeter functions and how to use the meter to test components on an HVAC System. The video made by AC Service Tech near the bottom shows a shorter version of how to use the Multimeter and test components. We have the G2 Phoenix Series Multimeter like what is used in the YouTube Videos for sale on the following page: UEi DL389B G2 Phoenix Pro Plus True-RMS AC Clamp Multimeter (With Temperature)  We hope these two videos help you to learn how to use a Multimeter. Thanks so very much to Word of Advice TV and AC Service Tech for making these two informative videos! If you have any questions please let us know by commenting below or emailing us. Our email is We would love to help you out and earn your business! 

You Can Search Our Site for More Troubleshooting Problems with Answers, Heating, Air Conditioning Parts and Supplies in the Google Search Box Below:

2 thoughts on “How to Use a Multimeter to Troubleshoot HVAC Problems.

  1. I have a carrier 9200. We have a programmable Honeywell thermostat and it quit working last night, and I’m low voltage at the terminals in my hallway.

    Per the video above, I confirmed 120 going all the way to the transformer, and 24V coming out. Ohm tested the fuse, it is good. Only 2.4V on the R terminal…that sounds like a bad board, correct?

    The trouble code has something about an igniter, but I would think if that’s the issue, I’d have no heat and correct voltages, so I’m inclined to think the board is friend and not to be trusted on its error codes. Thoughts?

    Thanks for this website, very helpful!

    1. Hi Preston!
      You should have 24 to 28 volts AC between the R and C (com) terminals on your control board and 24 volts between W and C (com) when the thermostat is calling for heat to be ON. If your furnace has a draft inducer the draft inducer should start first. If the draft inducer is not starting then yes you probably have a control board problem. We have a good video and a good explanation of the proper sequence of operation for a gas furnace on the following page: I hope this helps you find and fix the problem. If you would like me to look up parts then please send me your Carrier 9200’s product number to our email address: and I will be glad to look up any parts that you might need. I hope you can find and fix the problem soon! Steve

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