how to check bad ac contactor



Is your air conditioner not working properly? Is it struggling to cool your space or emitting warm air instead? The culprit could be a bad AC contactor. The AC contactor is a critical component in your air conditioning system that controls the flow of electricity to the compressor and the condenser fan motor. Over time, the contactor can wear out or get damaged, leading to poor AC performance. In this article, we will guide you on how to check for a faulty AC contactor and provide you with step-by-step instructions to help you diagnose and fix the issue.

What is an AC Contactor?

An AC contactor is an electrical relay that acts as a switch to control the flow of electricity in an air conditioning system. It is typically located inside the outdoor unit and is responsible for turning the compressor and condenser fan motor on and off. When the thermostat signals the air conditioner to start, the contactor receives a low-voltage signal from the control board, activating the high-voltage circuit to power the compressor and fan motor. If the contactor is faulty, it may fail to complete the circuit, preventing the necessary voltage from reaching the compressor and fan motor.

Signs of a Bad AC Contactor

1. Unresponsive AC Unit: One of the most common signs of a faulty contactor is an unresponsive air conditioning unit. When you set your thermostat to cool and lower the temperature, the compressor and fan motor should kick in to start the cooling process. If nothing happens when you adjust the settings, it may indicate a problem with the contactor.

A faulty contactor can interfere with the flow of electricity, preventing the AC unit from starting. In this case, you may hear a clicking sound or buzzing noise without the AC actually turning on. It is essential to address this issue promptly to avoid further damage to your air conditioning system.

To check if the contactor is the cause of the problem, you can carry out a visual inspection. Turn off the power to your air conditioner before proceeding with any inspection or repairs.

Inspect the contactor for any signs of damage or wear. Check if the contacts are pitted, burnt, or corroded. If the contacts appear blackened or charred, it indicates that the contactor has been overheating and needs to be replaced.

2. Intermittent Cooling: Another indication of a bad AC contactor is intermittent cooling. If your air conditioner works inconsistently, providing cool air sometimes while blowing warm air at other times, it could be due to a faulty contactor.

A failing contactor may fail to engage completely, resulting in the compressor and fan motor turning on and off randomly. This can lead to inadequate cooling or no cooling at all. If you experience inconsistent cooling, it is necessary to inspect the contactor for any issues.

3. Loud Clicking or Buzzing Noises: A malfunctioning contactor can produce audible clicking or buzzing sounds. When the contactor attempts to close or open the circuit but fails to do so due to damage or poor connection, it can produce unusual noises.

If you hear loud clicking or buzzing sounds coming from your outdoor unit, it is a clear sign that the contactor needs attention. A replacement may be required to resolve the issue and restore proper functionality to your air conditioner.

4. Stuck Contacts: Over time, the contacts in the AC contactor can become stuck or welded together. Stuck contacts can prevent the compressor and fan motor from turning off, even when the thermostat signals the system to stop.

To check if the contacts are stuck, turn off the power to your air conditioner, and carefully inspect the contactor. If the contacts are visibly fused together or have a welded appearance, it indicates a problem. Stuck contacts can strain the electrical components and lead to system damage. It is crucial to replace the contactor if you find any signs of sticking or welding.

5. Excessive Heat: A defective contactor can generate excess heat due to poor electrical connections or damaged components. If you notice that the contactor is unusually hot to the touch, it is an indication of an underlying problem.

When the contactor overheats, it not only affects its own performance but can also impact other electrical components in the air conditioning system. Excessive heat can cause further damage and may lead to costly repairs. Therefore, it is essential to address this issue promptly by replacing the faulty contactor.

Steps to Check a Bad AC Contactor

Step 1: Shut Off Power: Before inspecting or working on the AC contactor, it is crucial to turn off the power supply. Locate the electrical disconnect box next to your outdoor unit and switch it to the off position. You can also shut off the power from the circuit breaker panel.

Safety should always be a top priority when dealing with electrical components. Turning off the power will minimize the risk of electric shock and protect you from any potential harm.

Step 2: Remove Access Panel: Once the power is off, remove the access panel to gain access to the air conditioner's internals. The access panel is typically located at the side or top of the outdoor unit.

Use a screwdriver or the appropriate tools to remove the screws securing the panel in place. Carefully lift the panel and set it aside in a safe place.

Step 3: Locating the Contactor: With the access panel removed, you should be able to locate the contactor. The contactor is a black box-like component with several electrical wires connected to it. It is usually situated near the compressor and the condenser fan motor.

Take a moment to familiarize yourself with the contactor, its connections, and its position inside the air conditioning unit.

Step 4: Inspect the Contactor: Once you have located the contactor, visually inspect it for any signs of damage, wear, or corrosion.

Carefully examine the contactor's contact points or contacts. Look for signs of pitting, burning, or corrosion on the contacts. If necessary, take a photograph to reference later during the replacement process.

Additionally, check the contactor's coil for any visible signs of damage or burnt spots. Any physical damage to the coil can affect the proper functioning of the contactor.

Step 5: Testing the Contactor: To further verify if the contactor is faulty, you can perform a simple test using a multimeter.

Set your multimeter to the ohms (Ω) setting and touch the probes to two different sets of contacts on the contactor. The contacts you choose should not be adjacent to each other.

If the multimeter displays a resistance reading close to zero ohms or an open circuit, it indicates that the contactor is not functioning correctly. In such cases, it is advisable to replace the contactor.

Replacing a Faulty Contactor

If you have determined that your AC contactor is faulty and needs to be replaced, here are the steps to help you through the process:

Step 1: Purchase a Replacement Contact


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