blue and red swoop graphic

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. 


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.

Request Service

What Our Clients Think Of Us

Marlena PavloffMarlena Pavloff
03:03 06 Feb 24
I had Ricardo from Aztil come with his helper to do my vents. He was prompt and got to work as soon as they got here. He explained what he was doing as they went along and I could tell he was going above and beyond to give us a good job. We are extremely happy with the service we got and would recommend them for duct cleaning, to their air conditioning service and contract. Have been with them for many years and I still think they are the best around.
Susan PerhamSusan Perham
21:56 02 Feb 24
Dana and Johnny were polite, professional, and didn’t leave until they made sure everything was running correctly. I would recommend them to all.
Miriam PurcellMiriam Purcell
21:56 31 Jan 24
Dana & johnny did a perfect job here.
Deborah KurlanderDeborah Kurlander
17:26 27 Jan 24
Thank you Dana from Aztil! Dana analyzed and fixed our ac problem quickly. He explained the problem and was courteous and thoughtful.
Crissia CCrissia C
00:29 26 Jan 24
Kenneth is impressive! He is an excellent communicator, explains step by step the situation and what he will do to remedy it. He is extremely knowledgeable and kind! Thank you for your hard work, Kenneth! We will continue with Aztil because of top notch service like yours.
enmanuel gutierrezenmanuel gutierrez
18:25 29 Dec 23
I'm thrilled with the service from Aztil Air Conditioning, especially by technicians Nick and Kenny. They were punctual, neat, and extremely polite. Their expertise stood out as they fixed my AC, carefully explaining what they were doing and ensuring all my questions were answered. They were thorough and left my home clean after the job, showing exceptional skill and customer care. I highly recommend them for anyone needing AC services. Great job and a big thank you!
fer martinezfer martinez
18:24 19 Dec 23
Great company! I had an exceptionally satisfying experience, thanks to their quick response time and thorough service!Ramon was both polite and knowledgeable, he efficiently identified and fixed the issue in a short period of time. His efficiency not only highlighted his skill but also enhanced the overall positive experience.If you want a company that is honest and professional you need to give them a call! I definitely recommend Aztil 👍👍
Tanjala ThomasTanjala Thomas
04:52 18 Dec 23
Let me tell you about Dana my service tech this morning. I discovered around 8:40 last night that our A/C was not working. Placed a call and was advised that someone would call me back. Excited to say that at 8:03 am not the service center but my technician Dana called to let me know he was on the way. He arrived promptly, he Was very skilled, professional and he restored my a/c. I've been a customer for over 20 years and I will continue. If you are ever in need of A/C service or installation Aztel is the local company to contact.Dana thank you for your amazing service today.
Wolf LinkWolf Link
19:42 12 Dec 23
I’ve been an Aztil customer for quite a while now. From doing the maintenance to replacing my A/C, they are the best. Their employee Alejandro Molina came out to provide maintenance to my A/C, since we already knew we needed a new unit, he scheduled the installation and followed through til the day of to make sure everything ran smooth. The installers were great too. Came in and did the job.If you’re looking for a great company to work on your A/C, call Aztil!

Our Partners

  • Carrier logo
  • Honywell logo
  • Mitsubishi Elctric logo
  • York logo
  • American Standard logo
  • Amana logo
  • Heil logo
  • Trane logo
  • Maytag logo
  • Rheem logo
  • Ruud logo
  • Rheem Team logo
  • Daikin logo