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5 Signs of a Bad or Failing AC Compressor Relay

Ac Compressor Unit From Inside

Air conditioners are complex appliances to have around the house. Additionally, there are a lot of parts that need to function correctly for your unit to cool rooms efficiently. A faulty compressor relay can be a huge problem for your climate control device.

The compressor relay is also referred to as the contactor relay. It is one of the essential components of an aircon unit. The relay switch provides power to the compressor, enabling the unit to run smoothly when cooling your home.

Early detection of a stuck or bad relay can help prevent expensive repairs to the unit and ensure your house or office is cool during summer.

Unfortunately, it can be challenging to identify the issue. This post will look at some signs of a failing compressor relay.


If the unit has a failing compressor contactor or relay, the compressor might have trouble turning on; the air conditioner blows warm air or has inconsistent cooling in the room.

Furthermore, you might hear more frequent clicking noises from the compressor, and the unit will consume more energy.

Likewise, we will also look at ways to fix a faulty relay switch.

What Is an AC Compressor Relay?

Electric Starting Relay For The Compressor Of The Ac

Before getting to the symptoms of a faulty compressor relay, let us look at the component and what it does.

The relay or contactor is a switch that controls the power supply to the compressor. When the air conditioning unit cools down the room to the desired temperature, the relay switches off, automatically turning off the compressor. When the temperature rises, the switch turns on the power supply, allowing the compressor to pump coolant throughout the unit.

In addition to regulating the power supply to the compressor, the relay also plays a significant role in ensuring energy efficiency in your HVAC appliance.

5 Signs of Bad Aircon Compressor Relay

Compressor relays, like most electrical devices, can often burn out or fail after prolonged use. When the switch is stuck or about to fail, you might notice some issues with your air conditioner.

Let us look at some early signs of a bad compressor relay.

1. Compressor Is Not Running

Fixing Conditioner Using Measuring Equipmentc Filling Air Conditioner

If your compressor is not turning on and the circuit breaker is still on, you might have a problem with the relay.

An aircon compressor can be described as the unit’s pump. It sucks coolant from the evaporator coils and pushes it toward the condenser.

As previously mentioned, the relay supplies the unit with power. When the switch turns on, you will hear that familiar noise of your compressor running.

However, if the relay is stuck or faulty, the electrical circuit will not be complete, preventing the compressor from turning on.

2. AC Blowing Warm Air

Woman Feeling Warm Air From Ac

Another common sign of a failing compressor is warm rooms even when the AC runs.

If the compressor is not running, it cannot pump refrigerant to the unit’s evaporator coils. This affects the coils’ ability to absorb heat from the air. The air conditioner will end up blowing warm air around the house.

3. More Frequent Relay Clicking Noise

Woman Feel Annoyed, Suffering Noise From Ac

Thirdly, you might notice frequent clicking from the HVAC if you have a failing compressor relay.

Usually, when the compressor relay turns on, you will notice a slight clicking sound. However, the clicks occur more rapidly as the contactor tries to turn on the compressor and fails.

Apart from clicking noises, you might also notice rattling sounds as the relay struggles to turn on.

Weird Noises In Your AC

If you hear weird noises from your compressor, it might indicate something other than a failing relay. We recommend calling an HVAC repair professional to inspect the unit.

4. Inconsistent Cooling

Technician Repairing Air Conditioner

Likewise, you might also notice that your climate control unit inconsistently cools the house.

In case of a failing relay, the compressor might not receive enough power to circulate refrigerant into the unit. This might result in the unit having longer cooling cycles than usual, resulting in uneven or erratic cooling around the office.

5. Higher Energy Bills

Stressed Latin Man Looking At The High Electricity Bill

Lastly, a malfunctioning contactor can also lead to higher energy consumption.

When the switch is stuck, the air conditioner struggles to reach the desired temperature set on the thermostat. This results in the unit’s longer cooling cycles, leading to a spike in electrical consumption.

How To Fix a Defective Aircon Compressor Relay

Checking The Ac Compressor Motor Relay

Do you suspect that your AC’s compressor relay is failing? Faulty relays should be replaced as soon as possible to prevent further damage to the unit and ensure it functions properly. The switch should be replaced by a qualified repair professional.

Replacing A Bad Relay

An original equipment manufacturer (OEM) part should replace a defective compressor relay. It ensures that your unit runs smoothly and for a longer time.

Let us look at the procedure to replace a faulty aircon compressor relay.

1. Turn Off the Air Conditioner

The repair tech must turn off the AC to prevent electrocution during replacement. Go to the electrical panel and locate the circuit breaker connection for the unit. Switch the breaker to the “Off” position.

2. Remove the Protective Panel

The relay switch is housed under a protective panel. Before replacing the switch, the repair expert will remove the panel to access the switch.

3. Remove the Damaged Relay

Next, unfasten the screws that hold the contactor relay to the compressor using a screwdriver. Carefully move the switch to the side, ensuring not to damage the connection wires.

Helpful Tip

Do not remove the wires attached to the old relay switch. It makes it easier to track where all wires go in the new contactor after fastening it to the unit.

4. Install the New Relay

Now, take the new relay and install it on the AC panel.

5. Reconnect the Relay Wires

After fastening the contactor relay, you need to match the wire fittings from the old switch to the new one. Transfer each wire at a time so you do not get confused about which spot the connection should go.

6. Reinstall the Protective Cover

Ensure all the wires are securely fastened before putting the protective cover back onto the compressor.

7. Test the Aircon Unit

The last step is to turn on the HVAC unit at the circuit breaker and test if the compressor turns on.


Man Is Fixing A Heavy Air Conditioner

If your AC is acting up, you might have a problem with the compressor relay. The relay switch is responsible for regulating the power supply to the unit, turning it on and off depending on the room’s temperature.

When the contactor relay fails, you might notice that the compressor in your unit does not turn on, the air conditioner is blowing warm air or inconsistent room cooling. Likewise, faulty switches also tend to make clicking noises more often, and you might have higher energy consumption.

Replacing a defective relay switch is not your typical DIY project. You should always get a qualified AC unit professional to help.

Regular maintenance of your climate control device ensures that any issues with the contactor relay or the unit are identified early and prevent expensive repairs down the road.

Frequently Asked Questions

How Long Should an AC Contactor Last?

Most compressor relays can last between 5-10 years with regular maintenance. However, their durability depends on how often you use the unit and how often the outdoor unit is cleaned.

How Often Should You Replace an AC Contactor?

Most manufacturers recommend replacing the contactor relay at least once every 5-6 years. However, if you notice any signs of the relay failing, you should contact an HVAC professional immediately to inspect your unit.

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