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When someone mentions the term furnace transformer, you immediately assume it’s a large piece of equipment similar to those Autobots in the movies; however, it’s a device that serves a primary function to your furnace. The transformer is responsible for supplying power to the unit. Transformers essentially lower your home’s voltage output to ensure it’s within the standard 120 volts. If your furnace doesn’t operate efficiently, you could have furnace transformer problems.


Common Signs of Furnace Transformer Problems

While it is difficult for you to identify furnace transformer problems, you should look out for some visual signs. When you notice bulges or burn marks on the outside, the transformer is likely faulty or blown. Don’t test the unit by yourself but instead speak to a professional to conduct the necessary tests to ascertain what the problem is and the correct strategy.

Strange sounds are usually an indicator that something isn’t right. When you hear a droning sound, it’s perfectly normal from the transformer. However, if the humming is intense and accompanied by vibrations, it points to a faulty transformer. Bear in mind; there could be other reasons for the unusual sounds and vibrations, making it advisable to hire a competent technician.

A sure sign that your transformer is faulty is the continuous tripping of the circuit breaker. The reason it does this is to prevent a surge in voltage. If this goes on repeatedly, along with the blowing of fuses, it’s time to call for help.

Even with an appropriate power supply, the furnace may not be operational with a faulty transformer. It does this to protect the other components within the furnace. In this case, it’s wise to recruit a knowledgeable individual to investigate.


The Role of a Transformer

The transformer transfers electricity from one circuit to another through electromagnetic induction. It’s essential to increase or decrease the voltage to meet the capacity of other electrical components. The transformer changes the voltage from the circuit board into the HVAC unit. This process allows the fan and air conditioner to work together by cycling on and off. You can locate the transformer inside the furnace, but in very rare cases, you might find them outside.


Checking the Condition

While we always advise hiring a professional to handle these tasks, if you’re familiar with a multimeter and its function, you can determine if the transformer is faulty. If that is the case, it will deliver infinite readings. However, if there’s nothing wrong with the transformer, you should see a reading between zero to ten ohms.


Causes for Faulty Transformers

A power surge or lightning strike is enough to affect the transformer in your furnace, among other household appliances such as televisions, computers, and home audio systems. Components such as capacitors will suffer physical damage after a power surge. If you turn the circuit breaker off and on again after 30 minutes and the system doesn’t work, you have a problem with the transformer.

A faulty contactor is usually the primary reason for a defective transformer. The contactor is a relay that regulates the electricity within a system. The surfaces in the contactor can deteriorate over time, becoming oxidized and causing them to stick. As a result, the contactor doesn’t operate efficiently, and instead of cycling on and off, it sends current to the compressor and motor constantly, leading to burnout. Picture a vehicle’s engine running all the time; something is bound to go wrong at some point.

If there are loose wires inside your transformer, it can cause a short circuit that will fry the transformer.


Maintenance Makes a Difference

While you will schedule regular maintenance of your HVAC system, the technician must inspect the condition of your transformer. If there are signs of wear on the wires, you should change it immediately instead of neglecting the issue. Failing to take action will result in a faulty furnace that constantly turns off when you require it the most.

Ask the technician to check the secondary voltage since it follows the same process as testing for the supply voltage. The results of this test will inform you if you require a new transformer.



You should only attempt replacing the furnace transformer if you possess the knowledge and skills regarding HVAC systems. If not, you could end up damaging the unit and causing further problems for yourself. These mistakes can lead to expensive errors, especially if you have to install a new system.

If you come across the signs of furnace transformer problems, it’s advisable to call a professional to address the situation. Consequently, you can rest easy in the fact that they know what they’re doing, and they can catch potential problems early to prevent costly repairs or replacement in the future.