can a bad ac contactor trip a breaker


Can a Bad AC Contactor Trip a Breaker


Air conditioning units are a crucial component of modern living, ensuring comfort during hot summer months. However, when these units start to malfunction, it can be quite frustrating and inconvenient. One common issue that homeowners often encounter is a tripped breaker. While various factors can cause breaker trips, a faulty AC contactor is among the culprits. In this article, we will explore the relationship between a bad AC contactor and tripping breakers, diving into the details, causes, and potential solutions for this problem.

The AC Contactor: An Overview

The AC contactor is an electrical switch that controls the flow of current to the air conditioning unit's compressor and condenser fan. It works in conjunction with the thermostat, receiving signals that activate or deactivate the air conditioning system. When the thermostat senses a need for cooling, it sends a low-voltage signal to the AC contactor, which then allows high-voltage power to flow into the compressor and condenser fan. This action initiates the cooling process.

Understanding Breaker Trips

Breakers are designed to protect electrical circuits from an overload of current or a short circuit. When the flow of current exceeds the breaker's limit, it automatically shuts off the power to the circuit, preventing potential electrical hazards. Tripped breakers can be indicative of underlying issues within the circuit, and understanding why they occur is crucial to troubleshoot and resolve the problem effectively.

The Bad AC Contactor and Breaker Trips

When a faulty or worn-out AC contactor fails to open or close properly, it can result in a range of issues, including breaker trips. Here's how a bad AC contactor can lead to tripped breakers:

1. Excessive Electrical Arcing

One common problem associated with a bad AC contactor is excessive arcing. When the contactor's points become pitted or worn, the electrical current can arc across the damaged contact surfaces, generating heat in the process. This arcing can cause a sudden surge in electrical current, triggering the breaker to trip as a protective measure. Additionally, the heat generated from arcing can further damage the contactor, potentially leading to a complete failure.

2. Stuck Contact Points

Over time, the contact points in an AC contactor can become dirty or corroded, hindering their ability to make solid contact. This can result in the points getting stuck in either the open or closed position. When the contactor fails to open properly upon signal interruption, the current continues to flow, creating an overload and tripping the breaker. On the other hand, if the contactor gets stuck in the closed position, it can cause the compressor and condenser fan to run continuously, overloading the circuit and leading to a breaker trip.

3. Worn-out Coil

The coil within the AC contactor is responsible for engaging and disengaging the contact points. If the coil becomes weak or worn-out, it may not generate enough magnetic force to move the contact points efficiently. As a result, the contactor may struggle to make or break the electrical connection effectively. When the circuit remains closed for an extended period, it can lead to a surge in electrical current, causing the breaker to trip.

4. Contactor Coil Short

A shorted coil within the AC contactor can also be a contributing factor to breaker trips. A shorted coil occurs when the insulation on the coil windings deteriorates or wears off, allowing the windings to come into direct contact and create a short circuit. This short circuit can result in the breaker instantly tripping due to the abnormal flow of current.

5. Defective Contactor

In some cases, a bad AC contactor may simply be defective from the beginning. Manufacturing defects or quality issues can cause the contactor to fail prematurely or malfunction, resulting in electrical problems such as breaker trips. While less common, this possibility should not be overlooked when troubleshooting the issue.

Diagnosing and Solving the Problem

Now that we have identified the potential ways a bad AC contactor can lead to breaker trips, let's explore the steps to diagnose and solve the problem:

1. Observation and Visual Inspection

Begin by inspecting the AC contactor for any visible signs of wear, damage, or corrosion. Look for melted or burned areas, pitted contact points, and loose or frayed wires. Pay close attention to the condition of the coil, ensuring that it is intact and not shorted. If any issues are noticed, it may be an indication that the contactor needs replacement.

2. Testing the Contact Points

Using a multimeter, test the contact points for continuity. Ensure there is no resistance when the contact points are closed and that the circuit opens when they are meant to. If there is resistance or the circuit fails to open, it indicates a contactor problem.

3. Checking the Coil

Measure the resistance of the contactor coil using a multimeter. If the resistance is significantly higher or lower than the manufacturer's specifications, it suggests a faulty coil that needs replacement.

4. Cleaning or Replacing the Contactor

If the contact points are visibly dirty or corroded, clean them gently with a contact cleaner or emery cloth. However, if the damage is severe or the contactor shows signs of malfunction, a replacement is likely necessary. Consult an HVAC professional for assistance to ensure proper installation.

5. Professional Inspection and Repair

If the breaker continues to trip even after replacing the contactor, it is recommended to seek assistance from a professional HVAC technician. They can perform a comprehensive evaluation of the air conditioning system, including the electrical components, to identify any underlying issues that may be causing the breaker to trip.


A bad AC contactor has the potential to trip breakers, causing inconvenience and disrupting the functioning of an air conditioning unit. Understanding the relationship between a malfunctioning contactor and breaker trips is essential for homeowners and HVAC professionals alike. By diagnosing and resolving contactor-related issues promptly, individuals can restore the functionality of their air conditioning system and ensure uninterrupted comfort. Remember, safety should always be a priority, and when dealing with electrical components, it is advisable to consult a trained professional for accurate diagnosis and repair.


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