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Want to understand how to test a thermostat with a multimeter but can’t find a decent guide online? You’ve come to the right place!
I made it as simple as possible so you could quickly comprehend how to test your 24-volt thermostat, water heater, and/or defrost thermostat.
By the time you’re done with this guide, you’ll know if your unit is still in great shape.
Ready to learn more? Then let’s jump right into it!
How to Test a 24-Volt Thermostat
First in the list, I have a simple guide on how you can test your 24-volt thermostat.
1. Identify the Wires
Troubleshooting a thermostat will be much easier once you’re familiar with the wires on the unit. That said, here’s a list:
- C — this is the common wire
- W — this is the heat wire
- Y — this is the cooling wire
- R — this is the power wire
- G — this is the fan wire
2. Check the Voltage for the Fan
After understanding what each wire is used for, you should understand how to test a room thermostat with a multimeter. That being said, grab your multimeter and then set it to AC volts.
Next up, grab the leads, put red lead on the C wire, and then place the black on the G wire. Since we’re dealing with a 24-volt thermostat, your multimeter should display anywhere from 24 to 28 volts. However, keep in mind that this voltage might decrease if you’re not running the fan.
3. Check the Voltage for the Heat
Now that you’ve checked the G wire, check the heat one. So, go ahead and turn on the heat. After that, move the black lead from the G wire to the W wire. Once again, your multimeter should display the voltage on the screen. Anywhere from 24 to 28 volts is good.
4. Check the Voltage for Cooling
Now check for cooling. So, switch the thermostat to cooling. After that, put the black lead on the Y wire. When doing this, the multimeter will display the voltage it’s getting. If you’re not getting any voltage, the thermostat might still be on heat.
It can take up to 5 minutes before this option kicks in. But if you’re still getting no power, there’s probably something wrong with it.
If you’re a visual learner, watch this video:
How to Test a Thermostat on a Refrigerator
Having trouble with your thermostat on the refrigerator? I got you. Here’s how to test a thermostat with a multimeter:
1. Set the Meter to Continuity
Notice that your multimeter has several options. But in this case, turn the wheel to OHMs. The symbol for this setting looks like a WI-FI icon or a current going to the right.
2. Find the Opening & Closing Temperature
If you take a look at the side of your defrost thermostat, you’ll notice that it has a bunch of numbers and letters. For example, it could say: “L57 – 35 F.” The first letter and number refer to the limit temperature, which the thermostat uses to open up.
On the other hand, the last number is the closing temperature. However, to get that number, you have to subtract the limit temperature from the closing temperature. In this case, you would end up with 22 degrees Fahrenheit.
3. Check for Continuity When the Unit is Warm
Here’s how to test a fridge thermostat with a multimeter: grab both leads and place them on the defrost thermostat wires.
When the thermostat is warm, it shouldn’t show any continuity on the built-in screen. This means that the circuit inside the unit is open. Therefore, the multimeter will not make any sound.
4. Cool the Thermostat Down
You now have to cool down the thermostat below the temperature it’s supposed to close. That said, put it inside a working freezer and let it get cold for a while.
5. Check for Continuity
After cooling down the thermostat, it should have continuity. So, go ahead and put the black and red leads on the defrost thermostat. Your multimeter will pick up the continuity and show it on the screen. The unit will also make a sound, indicating there’s continuity.
Still, this doesn’t always mean that the thermostat is in great shape. So, look for these signs to make sure:
- The back looks bubbled — if the thermostat looks bubbled on the back, replace it.
- Wires look burnt — if the wires on the thermostat look burnt, replace the unit.
How to Test a Water Heater Thermostat
You don’t need a professional to test a water heater thermostat. Instead, you can do it at home with a cheap multimeter. Here’s how:
1. Getting Ready
Before getting started, please turn the range selection to the lowest setting for OHMs. Once that’s done, shut off the power to the water heater. Next up, remove the small cover from the water heater. After that, pull the protective cover from the water heater thermostat.
2. Disconnect the Power Wires
Notice the number of wires going into the thermostat. You have to disconnect them to isolate the thermostat from the circuit.
3. How to Test a Water Heater Thermostat With a Multimeter
After isolating the wires, put the black lead on one side of the terminal and the red lead above that terminal. Your multimeter should now indicate close to zero OHMs.
However, if the screen does not change, this means the thermostat does not have continuity and must be replaced.
That said, repeat this test on the other side of the terminal, meaning if you started on the left side, you must run the test on the right side. That way, you’ll know for sure if the unit is defective.
Frequently Asked Questions (FAQs)
Want to know more about thermostats? Then check this out:
How to know if my refrigerator thermostat is damaged?
- If your refrigerator’s temperature fluctuates randomly, you could have a bad thermostat. Moreover, if the unit does not have continuity when it closes, it must be replaced.
How do I know if my water heater thermostat is not working?
- Run a continuity test using a multimeter. You could either use an analog or digital multimeter. It doesn’t matter. If the multimeter shows no continuity, then the unit is defective and must be replaced.
How to reset my water heater thermostat?
- If you’re having trouble with a water heater thermostat, consider resetting the unit. To do so, remove the cover from the water heater and then find the thermostat. After that, press the red button.
How to know a thermostat is faulty?
- If the thermostat is unresponsive when switching modes, there’s probably something wrong with it. So, get a multimeter, hook up the leads to the wires on the thermostat and make sure you’re getting power on each cable.
There are many multimeters available, but you can get a cost-effective model and learn how to test a thermostat with a multimeter. As you know by now, troubleshooting a thermostat barely takes any time with my simple steps.
Once you understand the basics, you can test most things at home and save yourself some money. But as always, protect yourself before messing with electricity. This is no laughing matter, and you could end up with severe injuries.