what causes ac contactor to burn out


What Causes AC Contactor to Burn Out?

AC contactors play a crucial role in the proper functioning of air conditioning systems. These devices serve as switches that allow the flow of electrical current to initiate the cooling cycle. However, like any other electrical component, AC contactors can sometimes burn out, leading to system failures and costly repairs. Understanding the causes behind AC contactor burnout is essential for homeowners and HVAC technicians. In this article, we will explore the common factors that contribute to AC contactor failure and discuss the preventive measures that can be taken to prolong their lifespan. By gaining insight into these aspects, you can ensure the smooth operation of your air conditioning system and minimize the risk of unexpected breakdowns.

1. Electrical Overloading and High Voltage Surges

Electrical overloading and high voltage surges are among the primary reasons for AC contactor burnout. When the electrical load exceeds the recommended capacity of the contactor, excessive heat is generated, causing the internal components to deteriorate over time. Similarly, sudden voltage surges, either from the power grid or due to lightning strikes, can lead to contactor failure. These voltage spikes cause an excessive current flow, overwhelming the contactor and ultimately leading to overheating and burnout.

To mitigate the risk of electrical overload and high voltage surges, it is crucial to have a properly sized contactor that matches the electrical load of the air conditioning system. Additionally, the installation of surge protectors can help safeguard the contactor from sudden voltage spikes. These devices work by diverting excessive voltage away from the contactor, preventing damage from occurring.

2. Contactor Welding

Contactor welding, also known as contact welding or sticking, is another common issue that can cause contactors to burn out. This occurs when the contacts inside the contactor become welded or fused together due to prolonged arcing during switching operations. Welding typically happens when the contact plating wears off, exposing the base metals. When the contacts try to open or close, they momentarily stick together, causing the arc to sustain and generating significant heat. Over time, this heat can cause the contactor to burn out.

Contactor welding can be caused by various factors, including excessive voltage, poor contact pressure, or contamination due to dust or moisture. Regular contactor maintenance, such as cleaning and inspecting the contacts, can help identify early signs of welding. By addressing the root causes of welding promptly and replacing or repairing the affected contactor, you can prevent premature burnout and extend its lifespan.

3. Electrical Pitting and Corrosion

Electrical pitting and corrosion can significantly impact the performance and longevity of AC contactors. Pitting refers to small craters or pits that form on the contact surfaces over time, typically caused by repeated arcing during switching operations. These craters reduce the contact area, leading to increased resistance and generating additional localized heat. Likewise, corrosion occurs when moisture or contaminants penetrate the contactor housing, causing oxidation and degradation of the contact surfaces.

Various factors contribute to electrical pitting and corrosion, such as poor contact pressure, high humidity levels, and exposure to chemicals or pollutants. Regular inspection and cleaning of the contactor can help identify early signs of pitting and corrosion. Applying contact enhancers or protective coatings to the contact surfaces can also help mitigate these issues, minimizing the risk of burnout and ensuring optimal contactor performance.

4. Environmental Factors and Contaminants

The environment in which the air conditioning system operates can significantly affect the reliability and lifespan of contactors. Dust, dirt, and debris can accumulate on the contact surfaces, inhibiting proper electrical contact and causing overheating. Additionally, high levels of humidity can lead to condensation, which introduces moisture into the contactor housing and increases the risk of electrical pitting and corrosion.

To combat environmental factors and contaminants, regular system maintenance is essential. This includes cleaning or replacing air filters, keeping the surrounding area clean, and ensuring proper ventilation. Moreover, installing a protective cover or enclosure for the contactor can provide an extra layer of defense against environmental elements. These proactive measures help prevent the accumulation of contaminants and extend the contactor's lifespan.

5. Age and General Wear and Tear

Finally, age and general wear and tear are inevitable factors that contribute to AC contactor burnout. Over time, the internal components of the contactor, such as the coil and contact surfaces, deteriorate due to repetitive switching operations and exposure to electrical currents. As the components weaken, the risk of overheating and failure increases, leading to contactor burnout.

While age and wear and tear cannot be completely eliminated, regular inspections can help identify signs of deterioration and allow for timely replacement. It is recommended to follow the manufacturer's suggested lifespan for contactors and schedule preventive maintenance with a qualified HVAC technician. By staying proactive and replacing aging contactors before they fail, you can avoid inconvenient breakdowns and costly repairs.


AC contactor burnout is a common issue that can disrupt the normal functioning of air conditioning systems. Understanding the causes behind contactor failure and taking preventive measures can help minimize the risk of burnout and increase the contactor's lifespan. By addressing electrical overloading, protecting against high voltage surges, addressing contact welding, mitigating electrical pitting and corrosion, combating environmental factors and contaminants, and being proactive regarding age and general wear and tear, homeowners and technicians can ensure the reliable operation of their air conditioning systems. Regular maintenance, inspections, and prompt replacements when necessary are essential steps in preventing contactor burnout and avoiding unexpected system failures.


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