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How to Test a 24V Transformer: 2 Methods Explained

Home appliances such as doorbells and HVACs run on 24V. This lower voltage is provided via a transformer. If this transformer is broken, your appliances won’t function. But to make sure something is wrong you need to test the transformer first.  

How to test a 24V transformer?

You can do it simply with a multimeter. Start by setting the multimeter to ohms. And then touch the leads to the sides of the transformer. If you get the same reading for both sides the transformer is functional. But if either side gives an infinite reading, it’s non-functional.

In short, that is the process. You ought to keep reading to learn more about the process!

2 Methods of Testing a 24V Transformer

Testing the transformer is quite easy. And, there are 2 ways you can do it. I’ll be going over both in this article. 

Method 1: Testing Resistance 

This is the more accurate of the methods. But it will take some work prior to testing. I’ll break it down into 3 steps. 

Step 1: Taking out the Transformer

Get a screwdriver. Unscrew and remove electrical covers over the transformer. It’s best to follow your manufacturer’s instructions. Incorrect tampering can damage the transformer. 

Step 2: Setting up the Multimeter

The first thing you need to do is switch the multimeter to ohms. If you don’t have a multimeter, invest in one. You can even use a multimeter for checking certain car engine troubles

Next, you’ll have to set up the leads. Insert the red lead into the slot marked “ohm”. Once you’ve put the leads in, touch the two leads.

This will create a closed circuit. The closed circuit should read 0 ohms.

Step 3: Testing the Sides

Now, you’re ready to test the transformer. Place the leads on the primary side of the transformer. This will give you a reading. The reading will vary based on the type of transformer being used. 

Next, touch the leads to the secondary side. You should get the same reading. If either side reads an infinite resistance, then that side is dysfunctional. 

In case either side tests dysfunctional, you’ll be best served replacing the transformer. 

Method 2: Testing the Voltage Output 

You can also test the voltage. It’s easier to do but there are more variables involved. Here’s how you do it. 

Step 1: Accessing the Transformer

Open the electrical panel for your appliance. If it’s an HVAC opening the panel cover will disengage the power. You’ll have to manually hold down the safety switch. I suggest putting an electrical tape over it to keep your hands free. 

Step 2: Testing the Output

Once you’ve accessed the panel, trace the wires coming out of the transformer. Trace them to the main board. Disconnect these wires from the board and insert the multimeter leads into them. 

Your multimeter should read 24 V. If it does, then your transformer is outputting the proper voltage. In case there are problems despite the transformer being functional, check the input voltage. 

Connect the leads to wires coming out of the circuit breaker. If the multimeter reads 120V or 240V, then the system is functioning properly. Otherwise, there’s a problem with your incoming power. 

Compared to the first method this one is less time consuming and easier.

Replacing the Transformer

Let’s say your transformer is broken. You’ll need to replace it. But how do you do that? Don’t fret, I’ll guide you through it. 

Step 1: Safety Precautions

The first thing you need to do is ensure your safety. Any time you’re touching electrical wires, make sure the power’s off. Otherwise you’ll risk getting shocked.

Step 2: Identifying the Transformer

Next, you’ll need to get a 24V transformer. If you’ve not bought one before, get one of these:

Product 1 
Product 2

In my opinion, either of these will last long and provide value for their worth. Once you’ve bought the transformer, check the label on it. There will be multiple wires on the primary side. 

Which wire you use will depend on the purpose of the wires. Usually, the white wire is a common wire. The black, red and orange are for 120V, 208V and 240V respectively. Check carefully to see if the set-up on your transformer is different. 

Step 3: Strip the Wires

Depending on what you’re using the transformer with you’ll be using a different wire. The wires on the transformer will come stripped. You only have to cut and strip the ones coming from the wall. 

Get a wire cutter and cut half an inch from the end exposing the wire. This will give you enough exposed wire to wrap together with your transformer. 

Step 4: Putting It All Together

Now it’s time to tie it all together. Take the common wires and wrap them together. Then wrap it with a piece of electrical tape. Depending on your appliance, wrap another wire with the hot wire from the wall. 

This completes the connection on the primary side. Next, take the wires on the secondary end and wrap them with wires of corresponding colors.

These wires are interchangeable and it doesn’t matter which is hot or common.

And there you have it. You’ve diagnosed and replaced the transformer. 


Question: Can a transformer be used as both step-up and step-down?
Answer: Yes. The same transformer can function as both a step-up and step-down one. It depends on which side you use as the input. 

Question: Can the transformer overheat?
Answer: Yes. Transformers are especially prone to overheating. This is because the transformers create heat while stepping the voltage up or down.  

Question: How many volts does an HVAC need?
Answer: The average home HVAC operates on 220V or 240V. If you don’t have a 240V or 220V outlet, you’ll need to install one. 


You won’t need to wonder how to test a 24V transformer. I’ve answered the question perfectly. 

While carrying out the tests, remember to wear rubber gloves. And also make sure to turn off the power to the panel you’re working on. This will ensure your safety. 

And with that I conclude my take on the ways to test a transformer.