As we know, testing an AC contactor is very important to make the whole project go smoothly. How to check AC contactor? Users can test the AC contactor relay through the following aspects.

1. Contactor coil

It is necessary to check the rated voltage of the contactor coil, then connect to the matching power supply, turn on the switch and check whether the contactor is pulled in. Otherwise, there is faulty in the contactor coil.

Another method is to use a multimeter to measure the voltage of the contactor coil. It is a good idea to see the parameters of a new electrical contactor with the same power as a reference if users are inexperienced.

2. Contactor contact

If the electrical contactor can be pulled in and the three-phase power supply is normal, but there is a phase loss at the output end, which can be judged by measuring the voltage of any two phases of the three-phase. At this time, we need to check the main contact of the contactor to see if there is any wear and burn. If so, it is important to replace it in time.

3. The suction of the electromagnetic mechanism is insufficient

Insufficient suction is also a relatively common phenomenon. Usually, it can be pulled in. However, there is a phase loss at the lower end of the main contact. After external force is applied, the phase loss disappears. In this case, the contactor needs to be replaced in time. The phase loss of the motor happens when there is increased vibration, abnormal sound, increased temperature, decreased speed, increased current and a strong humming sound while starting so that it cannot get started. If the phenomena above occur, it is necessary for users to focus on checking the power supply as well as contactor relay for phase loss and replace it in time to avoid greater losses.

It is known that AC contactor is an on-off switch used in the AC power supply circuit to realize the function of making and breaking the circuit at a long distance. Nowadays, it is the fact that the AC unit contactor relay switch is most widely used in various control circuits where the contactor generally uses the main contact to make or break the main circuit and connect load and adopts auxiliary contact to execute control commands. In addition, AC contactor relay has many features, including under-voltage protection, zero-voltage release protection, reliable operation, stable performance, high operating frequency and convenient maintenance, etc.

Multimeter can be used to measure A1 and A2 of the AC contactor coil. If there is resistance, the circuit is good. However, if there is no resistance or there is infinite resistance, it is possible that the coil is damaged. When the AC contactor coil does not work any more, AC contactor relay switch replacement is necessary. How to check AC contactor? How to tell if AC contactor is bad? The results for checking AC contactor vary from different resistance values.

  • If the internal contactor coil has a certain resistance value, its resistance value is 0 when the internal switch is closed and its resistance value is up to the infinite when open, then it can be judged that the AC contactor will work normally.
  • If the resistance value of the inner contactor coil is measured to be infinite or zero, then the inner coil of the contactor is damaged.
  • If it is measured that the resistance value is zero when the contactor switch is open, then the contacts conglutination inside the contactor is damaged.
  • If it is measured that the resistance value is infinite when the contactor switch is closed, the internal contacts of the low-voltage circuit breaker are damaged.
  • If any one of the four groups of switches inside the AC contactor relay is damaged, it means that the contactor is damaged.

When the internal coil of AC contactor is energized, the internal switch contacts will be pulled in. On the contrary, when the internal contactor coil is powered off, the internal contacts will be disconnected. Therefore, when testing the AC contactor, it is necessary to sequentially test the resistance value of its internal coil as well as the resistance value of the internal switch in the open and closed states. Since it is a power-off detection for AC electrical contactor, it is necessary to press the switch contact button on the upper end of the AC contactor to force the contact to close for detection.

Peaco Support offers a wide selection of AC contactors for your needs, including 3 pole AC contactor, 4 pole AC contactor, AC contactor CJX2-1810, AC contactor CJX2-1201, 110V AC contactor, 220V AC contactor, 24 volt AC contactor, 48 volt AC contactor, 24V DC contactor, etc. And the contactor current is various for options, such as 30 amp contactor for air conditioner, 40 amp AC contactor, etc. Buy AC contactor on We will provide professional guide for testing an AC contactor as well as choosing suitable AC contactor relays for your applications.