What Is An Air Conditioner Contactor? How Does It Work?

What Is An Air Conditioner Contactor? How Does It Work?


Today we’ll be taking a look at the Air Conditioner (A/C) Contactor and its work principle.

Air Conditioner Contactors keep your Air Conditioner function smoothly. You may find them in various parts of your Air Conditioner unit but don’t know what they are?

What Is An Air Conditioner Contactor? Here’s a quick explanation.

An air Conditioner (A/C) Contactor is a small device responsible for controlling the electrical flow to one of your Air Conditioner’s components. Including the compressor, the condenser, and your system’s various parts.

Put another way:

Air Conditioner Contactors are devices that we use in multiple parts of the unit to provide or cut off the power supply to many parts of the Air Conditioner.

In the remaining article, we’ll discuss Air Conditioner Contactors deeply and you’ll find answers to some of your relevant questions.

Without any further ado, let’s swoop into the details.

Air Conditioner Contactors – What are they?

Air Conditioning Contactors control – either allow or block – the electrical flow in all parts of your A/C unit. You can take it as a switch that moves the power supply to different paths within the A/C system.

This trustworthy device knows the RIGHT time – when to permit electrical power to move along and when to stop the supply.

Amazing, right?

Different Types of Contactors:

Different types of contactors are used for different applications.

Here are the three types of contactors:

  • Single Pole Contactor
  • Double Pole Contactor
  • 3 Pole Contactor

They are rated for 120, 208/360, and 460 voltages consecutively. However, the coil voltage may vary.

1.      Single Pole Contactor

A single-pole contactor has to connect with one wire for power. The other leg is neutral and remains in the circuit. Always!

2.     Double Pole Contactor

A double pole contactor requires a connection with two power wires. It’s normally used in 208/230 Volt circuits.

3.     3 Pole Contactor

A 3 pole contactor needs to connect with three power wires for use in 460V, 3 phase circuits. Such types of contactors are found in commercial pieces of equipment and buildings. Only!

Did you know?

A double pole contactor is the most common Air Conditioner Contactor. And, almost every residential condenser – outdoor part of your A/C unit – uses a 208/230V contactor with a 24V coil.

How Do Air Conditioner Contactors Work?

The working principle of the Air Conditioner Contactors is a no-brainer!

Think for a moment:

What do you do when you need to turn on the light in your bedroom?

Flip the switch. Isn’t it?

The same goes for Air Conditioner Contactors.

 When you push the button of your bedroom’s light, you actually exert a little pressure. That pressure links the contact behind that push button, and your room lights up.

Now, how is this mechanism identical to the Air Conditioner Contactors work principle?

In a normal position – when your A/C is off – the contactors are in ‘UP’ position. That means they are blocking the electricity from reaching your unit’s main components.

When you turn the A/C on, what happens is:

The thermostat detects the temperature around. If it senses that the temperature of the surrounding is warmer than the set temperature of A/C, its switch develops a 24V connection with the furnace control board.

As a result, the fan turns on.

In the meantime, the furnace control board conveys the 24V signal to the 24V coil of the contactor. That coil energizes and pushes the button on the contactor. This ends in making contact on both sides of the contactors.

Hence, the path for the electrical supply is cleared off.

The electrical supply reaches out to the motor and compressor, and soon you get the chilly air.

See, it’s easy!

You might wonder what if the thermostat reaches the temperature we desire.

In that case, when the thermostat accomplishes its cooling goal, it sends another signal through a small voltage. And yes, that signal is to turn off the electricity supply.

Resultantly, the contactor lifts, and the power supply gets disconnected.

What can go wrong with Air Conditioner Contactors?

Just like any other electrical device an Air Conditioner Contactor can also fail to operate properly. The flawed conditions you can face are:

1.     A/C contactors can burn out.

Overheating or normal wear and tear can cause A/C contactors to burn out. If that happens, the component of the contactor responsible for supplying energy won’t turn on.

2.     A/C Contactors can get stuck.

An A/C Contactor can get stuck – either in ‘UP’ or in ‘DOWN’ position.

When stuck in ‘UP’ position:

The contacts won’t get the energy they need. Thus, they will not turn on – even when needed.

When stuck in ‘DOWN’ position:

The energy will keep flowing through the contactor constantly. Certain parts of your A/C unit might keep working when the rest of the system is shut down.

Signs Your Air Conditioner Contactor has malfunctioned!

If the A/C contactor goes bad your A/C loses the capability of cooling adequately.

When your A/C contactors get faulty, there are few signs it may show up.

●      Chattering:

An Air Conditioner Contactor chatters (makes a clicking sound) when it tries making a contact, but can’t. The reasons can be dirty contacts or a weak coil. 

●      Melting:

If you notice the plastic casing of your Air Conditioner’s Contactor is melted, that means you need a replacement.

●      Buzzing:

Is your A/C contactor making a buzzing sound but not triggering the power? This may be because your coil has gone weak or the contacts have gathered dirt.

Manually pushing the button may bring your A/C to normal functioning, but it’s RISKY!

Testing an Air Conditioner Contactor: Step by Step Process

Is your A/C system making abnormal noises?

The best way to identify the problem-causing part is to test your A/C. Grab the required tools and test your A/C.

The tools you need are:

  • A/C voltage Detector
  • Screwdriver
  • Multimeter
  • Phone or Camera

Step 1: Turn off the power.

First off, shut the electrical power to your Air Conditioner. Also, shut down the breaker to the furnace and make sure there is no voltage to the furnace.

You can do so by using an A/C Voltage Detector. This testing will reduce the risk of electrocution.

Step 2: Unscrew the side cover of your Air Conditioner.

Get to your condenser unit. It’s time to make use of your screwdriver to loosen up the screws of your Air Conditioner’s side cover.

Once done, you’ll be able to see the Air Conditioner’s contactor and its adjacent cables.

Step 3: Click a picture.

Click a picture to make sure you remember the position of the wires. Take as many pictures as you want – and from various angles!

Step 4: Remove the contactor and unplug the wires.

Use your screwdriver to take out the contactor. Also, disconnect the corresponding wires carefully.

Step 5: Test your Air Conditioner Contactor.

Set your Multimeter to OL setting.

Connect it to the low volt terminals on both sides of the contact.

If the reading is between 5-20Volts, your contactor is working fine. Contrarily, if the reading is lower than the said voltage or you see no reading at all – you need to replace the contactor.

 Step 6: Replace the A/C contactor.

Buy yourself a new A/C contactor or reach out to any HVAC technician to replace your contactor.

Planning to replace it by yourself?


What it takes is: A little time and a lot of care.

You can use the picture(s) you took to rewire the new contactor. Reinstall the side cover of the condenser and turn on the power of your A/C.

Avoiding Air Conditioner Contactor Problems:

Now that you know the symptoms of a troubleshooting A/C contactor and are well-versed with the replacement steps, you need to know how to avoid these problems?

The key to prevent your A/C contactor troubles is to keep A/C parts in a good shape. All the time!

You must schedule an annual tune-up of your A/C by an expert technician.

During the tune-up, the technician will inspect your cooling system’s contactors. A technician does the following:

  • Inspect all of your system’s electrical components – including the contactors
  • Clean off the built-up dirt
  • Replace worn out contactors when necessary


Your Air Conditioner Contactor connects or disconnects the power when it receives a command from the furnace and thermostat.

In all three types of contactors, you need a double pole contactor for your A/C system.

It works like a drawbridge – closing and allowing the power supply to pass through.

An A/C contactor that goes bad shows some signs like:

  • Chattering
  • Buzzing
  • Melting

In such situations, testing the A/C contactor is the way out. Examine your unit’s contactor and replace it – if needed!

Remember! Your safety has to be your priority. Never perform testing or replacement in unsafe conditions.  If so, call an HVAC technician at once.

Have any questions about something you read?

Go ahead. Leave me a comment below, right now!


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