Expert’s Guide: How To Test Relay With Multimeter

A relay is an electric switch whose purpose is to turn on a device with more electricity requirements. They are used in various electronic devices thanks to their compatibility. A relay easily fits in casings of different sizes, which makes them highly beneficial. They do not take up much space, but they provide enough power to the unit.

Relay switches are also used in air conditioners and other such appliances. However, they must be checked regularly to ensure smooth operation and no issues. This article will guide you through using a multimeter to check a relay. You will find out why and how to do so.

If you wish to learn more about air conditioning, please visit American Home Water & Air.

What is a Multimeter?

A multimeter is a device used to measure different electronic properties. This includes voltage, capacity, resistance, and so on. It is a small device that fits in your hand, and it can be either digital or analog.

A lot of electricians prefer using this tool when working with machines, appliances, etc. A multimeter consists of several parts, including red and black leads, a scale, needle, three ports, knob, etc. Did you know that a multimeter is the only necessary tool to test the functionality of a relay? Stick around to learn more about this!

How to Test a Relay with a Multimeter?

As the name suggests, a multimeter has multiple purposes, and one of those is to test relays. Relays are commonly used in electrical circuits–opening and closing them to let the electricity go through.

To ensure that it’s operating accurately, testing and maintaining a relay is of utmost importance. Here are the best ways to test a relay with a multimeter:

1. Measure Contact Resistance

Contact resistance is of great importance for a relay. It can tell you whether the relay is capable of carrying the current between two contacts. Although it can be measured in different ways, the most common and effective one is to use a multimeter.

A relay uses two contacts: open and closed. If the relay has enough power, the open contact will conduct, and the closed one will stop conducting. Once you place the multimeter, you need to put a particular voltage on the relay coil.

Make sure that when the relay is on, it functions as described above. If it is not on, it will do the exact opposite. You will also hear a sound coming from the relay as you turn it on. If none of this happens, it is a sign that your relay is broken and needs replacement.

2. Check Coil Resistance

The purpose of checking the coil resistance on a relay is to determine whether or not the coil is open. Sometimes, the voltage in the coil is higher than it should be, which causes such issues. You can check the usual voltage in the datasheet.

Another thing for you to check in the datasheet is the resistance value of your coil. It is generally under 400 ohms, but you still need to be sure. The reason for doing this is to compare the resistance value of the coil and the one that shows up on the multimeter.

Measuring the resistance with a multimeter is relatively simple. Set up the desired unit of an electrical circuit on the device, place the probes on the coil, and measure!

If you notice any difference between the datasheet value and the one on the multimeter, this could mean that your relay is broken. If the values are the same, you should have no problems!

3. Measure Current

Current is crucial to the proper operation of the relay; hence measuring it is of high importance. The best way to do so is with a digital multimeter.

Measuring the current is basically monitoring the electrons’ flow within the circuit. In order to get the flow’s level, you need to place the meter inside the circuit so that it picks up the current. While you measure the current, ensure that the resistance is as low as possible. You need to do this to avoid the multimeter from altering the current.

Once you start measuring, you will hear a sound coming from the relay. This is when you need to pay attention to the voltage and the current. Do this more than once to get the most accurate results. If the voltage is not high enough, it indicates that your relay is not working properly.

4. Test Terminals

There are four pins or terminals on a relay. They are generally found in two different groups: normally closed and normally open. There are also common terminals.

To check the normally closed relays, place the probes on normally closed and common terminals. Make sure the multimeter is set to a particular measuring unit, which is generally ohms. If the resistance value is at zero, it would mean that your relay is working just fine.

The process is almost the same when checking the open relays. In this case, you have to place the probes on the normally open and common terminals. The rest of the process remains the same. However, the resistance needs to be above zero (but not too high) if your relay is working properly.

5. Test Continuity

Firstly, make sure that you turn off the power when testing continuity on a relay! Once your safety is ensured, you can set your multimeter to check continuity.

The multimeter will show you the number ‘1’ before you start the process. You need to connect the probes to the two ends of different cables for the multimeter to start reading.

Next, you will hear a sound, and the device will show you a number apart from ‘1’. If the value remains the same, it would mean that there is a problem with the relay.


Relays are electronic devices that send more power to appliances such as air conditioners. As they are almost always operating, they tend to malfunction. That’s why it’s crucial to do regular check-ups on your relay.

There are several components that you need to check. The best way to do so is to use a multimeter. Make sure that your relay is operating as it should by testing it on time!

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