Reasons For Burning Of Contactor Coils

Reasons For Burning Of Contactor Coils

Contactors are electromagnetic switches that open-closed contacts and close open connections when energy is delivered to the coil ends. Different electrical problems can cause contactor coil failure. The insulation between the coil wires can deteriorate, resulting in a short wall-mounted AC unit. It’s also possible for the coil to become trapped in the open position.

Various Factors Cause Contactor Coils to Burn:

  • Voltage: When the voltage provided to the contactor coil is lower or more significant than usual, the coil may burn. When the coil starts burning, voltage and frequency should be examined first, and a stable coil voltage for the contactor should be provided. The coil must be supplied at the voltage and current values mentioned in the catalog to avoid coil burning.

  • Length of the control circuit wire: Control (coil) circuit wires that are too long can cause issues. Long cables are difficult to shut due to the considerable voltage drop across the cable, while cable capacitance with an enormous cross-section prevents opening.

  • Dust: Dirt or foreign particles in the contactor, especially in the wall-mounted AC unit, and harsh climatic conditions and corrosion can prohibit the contactor from closing, mainly when using the remote control. When this happens, the contractor should be cleaned with a strong clean airflow to remove dirt and dust, the circuit should be checked, and any conductive factors should be removed.

What Happens to the Contactor Coil if There is a Short Circuit?


If there is an overcurrent or short circuit in the supply network or the contractors are not used according to the technical data, malfunctions may occur. Contactors, in general, are circuit components that do not fail readily. If more current is sent through the main power connections than they can handle, the contacts will overheat and may stick due to the warmth. Contact selection should be based on the load sent via a contactor.

How to Avoid AC Contactor Coil Burnouts Through Maintenance?


In general, Mitsubishi ductless AC units contractor coil maintenance is separated into two categories: run-time care and inactive maintenance, as shown below:

  • Run-Time Maintenance

Ensure that the load current is within the normal range during regular use and that the relevant indications follow the typical circuit indicators. During operation, listen for strange sounds like chatter, humming, or buzzing, as noise is a sign of poor contact or under-voltage. 

Keep the contactor clean both inside and out, and make sure the contact points aren’t discolored or the coil isn’t burned out. Keep moisture, dust, grease, and physical obstacles away from the contactor’s complete closure and restrict vibration to avoid a poor operating state in the surrounding environment.

  • Inactive Maintenance

Ensure that the cable is secure, the wire insulation is intact, and no loose ends are present. If the contact is open, look for any signs of burns. Ensure that the interphase insulation resistance of AC contact is appropriately measured and that it does not fall below 10. Contactors should be cleaned at least once a year. Determine the contract’s reliability, the coil’s endurance, and the function of the middle spring. Look for open welds, burns, or discoloration on the contactor coil.

Dr. Ductless Heating and Cooling have provided excellent services in Los Angeles, Manhattan Beach, CA, and surrounding areas. Call us at 213-916-0005 for any inquiry about Mitsubishi ductless AC units.


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