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What Are The Symptoms Of Bad HVAC Transformer

By Aztil –

 The HVAC system is the heart of your household. It is a machinery which consists of many big and small parts. In machinery as complex as that occurrence of a fault is normal. What is important is that you deal with them promptly and efficiently. The local HVAC company is your best answer. However, being a little proactive, you too should know a little about the things that could go wrong with your HVAC unit. If you have at least some basic knowledge, nobody would be able to fleece you easily. In our bid to educate you about the issues you could face in relation to your HVAC, today we shall deal with the transformer . The transformer of the HVAC unit is also susceptible to developing faults. But how can you be sure of that? This post will help you understand a bit more about transformers and also tell you about bad transformer symptoms in HVAC.

What Is A Transformer?

A transformer is a device which can increase or decrease the voltage of an alternating current or AC. It is a passive device which transfers electrical energy from one circuit to another. This is achieved through electromagnetic induction.

Role Of HVAC Transformers

Transformers are used when the incoming electricity voltage needs to be either raised or lowered to meet the requirements of the other electrical components or parts. The work of a transformer is to change the voltage that travels from the circuit board to the HVAC unit. This progression allows the air conditioner and the fan to work in synergy while cycling on and off. The usage of Electricity can be amplified or diminished depending on how much power is needed.

Where Is The Transformer Located?

In an HVAC unit, the transformer is located inside the furnace. But in a few cases, which is less than 10%, it can be found inside the AC unit situated outside.

Bad Transformer Symptoms In HVAC 

There are a couple of things which are indicative of a bad HVAC transformer. These are –

1. Humming And Vibrating – The humming sound in transformers is normal. It is produced due to the expansion and contraction of the laminations or the iron core. However, if there is a drastic increase in this sound, accompanied by strong vibrations, it is indicative of a bad transformer in your HVAC unit. There could be other possible causes of the humming sound and the vibrations like incorrect installation or a faulty capacitor. So, it is best to let a technician come and check out where the real problem lays.

2. Tripped Circut Breaker – When the transformer of your HVAC unit goes bad, the circuit breaker will usually trip. It trips so that there is no surge of voltage. A voltage surge can fry various parts throughout the furnace and AC causing a major breakdown of the said equipment. 

3. HVAC Not Working – With a bad transformer, your HVAC unit will not work even when it has an adequate power supply. This is a protective mechanism to save the unit from severe damage.

There is no sure-shot way of confirming that the HVAC unit is malfunctioning due to a fault in the transformer. This can only be discovered through the elimination method. The HVAC technician will start with the most probable and simple causes which could prevent the unit from functioning. When nothing else works, they will tackle the bigger causes, one of which being a bad transformer. 

Checking The Transformer Is Bad

Your HVAC unit is not working, and you have worked your way through all possible causes. Nothing seems to solve the problem. It’s time to call in the reinforcements who can validate your findings and look for the real problem. The things you were attributing to a simple problem could actually be bad transformer symptoms in the HVAC unit. In order to confirm that the problem is indeed the transformer, you need to check it. For this, you need a multimeter, as well as the basic knowledge of using it. A faulty transformer gives an infinite or wide-open reading while a transformer without any fault reads between zero to 10 ohms which is indicative of a closed circuit. 

Causes Of A Bad Transformer

Bad transformer symptoms in HVAC unit may appear due to the following reasons –

1. Bad Contactor – More often than not, it is a bad contactor which leads to a blown transformer. A bad contactor puts the entire unit under a lot of stress. When the tension or strain becomes too much for the unit to handle it mostly results in a blown transformer.

2. Wiring Issues – Loose wires or cables inside the transformer can cause a short circuit due to which the transformer may fry.

3. Power Surge – An electrical failure in the form of a power surge can also cause transformer failure. 

Can I Replace The Transformer In My HVAC Unit?

If you are a trained technician who knows the ins and outs of a transformer, you can definitely do this job yourself. However, if you are not, you better think twice before taking on the job. Ask yourself whether it is worth paying a trained technician to do the job correctly? Or you are willing to foot the bill for a new HVAC unit if you make a hash of things? The answer will lead you in the right direction. 

Conclusion

Time and again, electrical equipment malfunction. The good thing is that a malfunction does not mean you need to buy a new one. Today, you can simply replace the faulty or the bad component and your machine will be as good as new. HVAC units are no different. You can replace the part that has fried or melted, and once that is done, it will start functioning as normally as before. A few things to keep in mind are – take good care of your HVAC unit through regular maintenance and try to refrain from carrying out any repairs yourself. 

If you are not careful, you may do more harm to the unit and maybe even get hurt or injured. There are people who are trained to care of such things, and they even have the necessary tools and replacement parts to complete the job quickly. Book an appointment with your local HVAC company if your unit is behaving abnormally. They are the most trusted people to take care of things immediately.

Frequently Asked Questions

If your transformer is bad, you will have a tripped circuit breaker. It tips to prevent a voltage surge which can fry various parts inside the HVAC system resulting in a major breakdown of the equipment.

Similarly, a transformer with clear burn marks or a bulged exterior is also a sign of a bad transformer.

You may face any of the following issues when the furnace transformer goes bad:

1. There is a loud humming sound coming from the unit with a dramatic increase in vibrations.

2. The circuit breaker trips frequently.

3. The unit stops working correctly even with an adequate power supply.

You can test an HVAC transformer using a multimeter. First, switch the multimeter to “Ohms.” Next, disconnect the electricity from the transformer. Now attach the multimeter and check the ohms reading for the primary and secondary windings. Ideally, the reading should be between 1 to 10 ohms. If it is higher, the HVAC transformer is bad.

There are several reasons that could lead to the HVAC transformer failure. Some common causes are corrosion, wear and tear, overloading, power surge, fluctuations, moisture, strong winds, rain, and lightning strikes.

Mostly, the transformer will burn when the load on it becomes too great. Sometimes sunlight on wires rots the insulation and shorts them. The other probable reasons are loose wiring, worn-out parts, and the accumulation of dust on the transformer.

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I've been using Aztil for over 20 years across 4 homes in Florida. From general services to complete A/C replacements, I wouldn't trust anyone else. My recent service in Port St. Lucie with Nico was excellent and he was very helpful in going over all of my HVAC system and answered a few questions I had.
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I cannot speak highly enough of our super kind technician, Randy, who came out to assess our AC today. Randy took the time to walk us through photos of the issues in our AC and offered to take care of it ASAP as he already had the parts in his truck - LOVE the preparedness! Aztil Air Conditioning is superior and we will request Randy on a go forward basis.

UPDATE 6/17/25 - Exceptional Service from True Professionals - Highly Recommend!

We recently had our ducts cleaned and sealed, plus our dryer vent serviced by Jordan and Hero from Aztil Air Conditioning, and I cannot say enough good things about their work. From the moment they arrived, these two demonstrated exactly what professional service should look like.

What impressed us most was their commitment to education - they took the time to walk both my husband and me through every step of the process, explaining not just what they were doing, but why it mattered for our home's efficiency and air quality. It's rare to find technicians who are so patient and thorough in their explanations.

Beyond their technical expertise, Jordan and Hero showed genuine respect for our home and our comfort level throughout the entire job. They worked with care and consideration, treating our space as if it were their own. As homeowners, we've all had those experiences where workers leave you feeling uneasy - this was the complete opposite. We felt completely at ease having them in our home.

Their professionalism, kindness, and attention to detail set them apart in an industry where those qualities aren't always guaranteed. If you're looking for HVAC services you can trust, don't hesitate to call Aztil Air Conditioning. Jordan and Hero will take excellent care of you and your home.

Five stars - we'll definitely be calling them for any future needs!
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Today I had a repair/replacement done by Alex Molina
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If anybody needs work and is lucky enough for Alex Molina to be your tech all will be done right
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Jordan & Herolson did a great job cleaning my ductwork. They arrived on time, were very nice, polite & efficient. Jordan explained everything clearly. They cleaned up thoroughly when they were done. The popcorn from my ceilings was everywhere, but they took care of it. Five stars.
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June 2 2025 Thank you Cody! It is a relief to finally have the A/C back to what it should be. The replacement of the coil is probably what was needed a month ago. Rather than dwell on what was, I truly appreciate the replacement service and how kind you were to a grieving widow.
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This is the second time Michael King has serviced my AC for AZTIL. He is always pleasant and courteous. He explains all he does to the unit and answers all questions I may have. He is very thorough. Great asset to the company. The trainee (Skyler) with him today has a very good teacher and seems to be on his way to being a positive service tech.
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I had woken up to no ac in my house. I contacted aztil on a Saturday at 5 pm and their technician called me back within a half hour. His name was Tino, he said that he would be there within 30 minutes…. And he was! He figured out the problem in 10 minutes and he solved it! Excellent service! Thank you so very much!
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Hey I need to update this 5 Star review, it needs to be a 10…. We needed a new system, boom, done in one day! Our tech, Asiel Barreto was tremendous. He even worked us through the process of using a NEST thermostat- Jackie in the central office rocked us through all the paperwork. This is why we are Aztil for life!
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Dana & Michael did an excellent job replacing my drain lines. They arrived on time & worked hard to finish the job in record time so I was without air conditioning in 1/2 the time expected!
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