How To Test A Furnace Transformer

DIY troubleshoot furnace transformer YouTube
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How to Test a Furnace Transformer


A furnace transformer is a crucial component of a heating system, responsible for providing the necessary voltage to power the furnace and ensure its proper functioning. Over time, transformers may experience issues or fail, leading to the need for testing and potential replacement. This article will guide you through the process of testing a furnace transformer to ensure it is working correctly.

Tools and Materials Needed

Before beginning the testing process, gather the following tools and materials:

  • Multimeter
  • Screwdriver
  • Wire strippers
  • Insulated gloves

Safety Precautions

When working with electrical components, it is essential to prioritize safety. Before testing the furnace transformer, make sure to:

  • Turn off the power supply to the furnace.
  • Wear insulated gloves to protect against electric shocks.
  • Handle all tools and wires with care.

Testing the Transformer

Follow these steps to test the furnace transformer:

Step 1: Disconnect Power

Turn off the power supply to the furnace by switching off the circuit breaker or removing the fuse.

Step 2: Locate the Transformer

Identify the furnace transformer, which is typically located near the furnace or within the control panel.

Step 3: Inspect the Transformer

Visually inspect the transformer for any signs of damage, such as burnt wires or a cracked casing. If any damage is present, the transformer may need to be replaced.

Step 4: Measure the Voltage

Set your multimeter to the AC voltage setting and touch the leads to the primary and secondary terminals of the transformer. The primary terminals receive power from the electrical source, while the secondary terminals supply power to the furnace. The multimeter should display the voltage reading for each set of terminals.

Step 5: Compare Readings

Compare the voltage readings to the specifications provided by the furnace manufacturer. If the readings are significantly lower or higher than the recommended values, it may indicate a faulty transformer.

Step 6: Test for Continuity

To ensure proper functionality, check for continuity between the primary and secondary terminals. Set your multimeter to the continuity or resistance setting and touch the leads to the corresponding terminals. If there is no continuity or a high resistance reading, it may indicate a problem with the transformer.

Step 7: Inspect Wiring

Examine the wiring connected to the transformer for any loose connections or damaged wires. Tighten any loose connections and replace any damaged wires if necessary.

Step 8: Reconnect Power

Once you have completed the testing and made any necessary repairs, reconnect the power supply to the furnace.


Testing a furnace transformer is essential to ensure the proper functioning of your heating system. By following these steps and taking necessary precautions, you can identify any issues with the transformer and address them accordingly. If you are unsure about performing the testing yourself, it is recommended to seek assistance from a professional HVAC technician.