How to Test a Furnace Transformer
- 1). Locate the transformer. It is a small rectangular box with incoming wire connections on one side labeled as "line" and outgoing wire connections labeled as "load."
- 2). Touch the voltmeter probes to the "line" connections of the transformer. The reading should be between 110 and 120 volts. If the reading is less than 110, you have a power source problem that needs to be repaired before you can accurately test the transformer.
- 3). Touch the voltmeter probes to the "load" connections of the transformer. This reading should be between 24 and 28 volts. If the reading you took on the line side was in the 110-120 volt range and this second reading is not between 24 and 28 volts, then you have a faulty transformer that needs to be replaced.
