Home AC Compressor Not Turning On [Solved]

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If you are dealing with a home AC compressor not turning on, then this article is for you. In this article, you can expect to learn about common issues that can prevent your ac compressor from working. And because we hate to leave you with no solutions, we have provided possible solutions for every issue.

ac compressor not turning on
A typical home ac compressor setup

There are a few things that can cause your air conditioner compressor not to turn on and these include:

  • Power issues
  • Defective ac contactor
  • Dead compressor capacitor
  • Defective starter relay
  • Thermostat issues
  • Bad wiring

Read also: AC Compressor Working but Not Cooling [Solved]

5 Reasons for Your AC Compressor Not Turning On

Let’s jump right into things that can stop your ac compressor from turning on.

1. Power

If you notice your compressor not working after turning on your thermostat, there could be a power cut to your outdoor unit. Head over to check your condenser unit and find out if both your compressor and the fans are not working.

If the fan is not spinning as well as the compressor not running, check the disconnect or power switch on the wall near the refrigerant line’s entry into your home. A disconnect cuts power from your condenser unit when you remove a small metallic plate. It can also disconnect power when you insert it upside down.

If the disconnect is in the right position but no power getting to your ac outdoor unit, then check the electric circuit breaker box for any tripped switches.

In the electric breaker box, check the switch labelled air conditioner, which is a switch for your ac outside unit.  If its in the middle position, then its tripped and you have to reset it. Otherwise, if the breaker for your unit is not tripped, you need to go and inspect your compressor housing once more.

More Power Issues

  • If the power switch for your indoor handler is accidently turned off.  The control board will not work and will not send the 24 v to the contactor (we’ll shortly be talking about a contactor) in your outdoor ac unit.
  • Blown out fuses: Check the control board inside your indoor unit for any blown out m3 fuses. It’s worth noting that if you have blown out fuses there could be something else going on that probably blew them up.

2. Defective AC Contactor

A defective ac contactor can prevent your ac compressor from turning on. After looking at your disconnector, power switches and breakers but your compressor is still not turning on, go on to check your outdoor unit.

contactor set up
Typical ac contactor set up

To open the ac outdoor unit, you’ll need a screwdriver. Open the part where power cables attach to your condenser unit.

What can go wrong with your ac contactor?

An AC contactor is a small device that completes the electrical circuit for your condenser unit. It has a coil and receives 24 volts power from your indoor air handler. When there is calling for heating or cooling, a magnet is activated and pulls together two metallic plates to complete a circuit.

Over time, the contactor can develop issues and malfunction. Newer models of the contactors have a better design that can prevent bugs or other things to stick between the contacts.

 In older models, objects and bugs would stick in the contactor and that would prevent the contacts from completing the circuit. If the circuit is not completed, both your compressor and your fan won’t turn on.

A contactor can get stuck in one position. Sometimes, it can stick in the down position and other times in the up position. If it gets stuck in the down position, you will experience your fan and the compressor running through out.

And when it sticks in the up position, your fan and compressor will not turn on even when you turn on your thermostat.

What can I do about a defective contactor?

While looking at your contactor use a screwdriver to manually push down the contactor plate to touch the other plate. If doing that starts your unit, then the problem could be with the contactor but if nothing runs, something else could be going on. It’s a good idea to get a new contactor if it has any problems because chances are, it will develop issues again soon or later.

AC Contactors are not expensive and can cost about $10 to buy online. Just take note of the type of contactor you have. You can either have a single pole contactor or a dual pole contactor.

PS NOTE: Before disconnecting your contactor, make sure you take a photo of how wires are connected so you don’t have any problems connecting your new contactor.

Read also: Fan Kicks on But Compressor Not Working [Solved]

3. Defective Capacitor

When an AC capacitor is defective, it won’t start your compressor or fan motor. Capacitors give starting energy to your compressor or fan motor. In the past, older ac compressors had separate capacitors for the compressor and for the fan motor.

bad capacitor
In the first photo: normal capacitor. In the middle and right photo: defective capacitor

This is not the case anymore with newer units.  Newer ac units come with dual capacitors which are able to power on one side, the compressor and on the other side the fan motor.

However, when one side of a dual capacitor stops functioning, then it won’t be able to provide power to the respective motor. Let’s say, a part that powers the compressor stops working, then the compressor won’t be able to turn on.

How do I tell my ac capacitor is dead?

Sometimes you can tell if your capacitor is dead by looking at it. A capacitor that has a bulged top is a clear sign that it is defective.  You might also hear humming sound coming out of your outside ac unit. This sound could be coming from a compressor that is trying to access power from a non-operational capacitor.

However, other defective capacitors may not even show any signs at all. It is better to use a multimer to test if your capacitor has continuity. If you prefer going for the later, ensure that you discharge your capacitor of any voltage before tapping your hands on anything

And it’s always best to wear gloves when dealing with any electrical problems to prevent shock.

How do I fix a defective capacitor?

I love to say this, ‘a capacitor can’t be fixed’, when its defective, you’ll need to replace it with an operational one. These days capacitors are readily available in the market and with just a click by your fingertip you can order it online in no time. You can buy a capacitor online for about $15.

When you choose to buy and replace an ac capacitor yourself, you can save about $150. That is, when compared to how much it would cost you if you had hired someone to do it for you.

TIP #1: If you choose to replace a capacitor yourself, take a photo of your capacitor wiring before disconnecting it, taking note of what wires go on what terminals.

TIP #2: Take note of your capacitor model. You can even use the model number to search for it online. For example, if you want to buy it on Amazon, just type the model number in the search bar and it should bring you a list of capacitors for that model.

4. Bad Starter Relay

A non-operational starter relay is another reason why your home ac compressor won’t kick on. A non-functional starter relay will not transport power from the capacitor to the compressor or to the fan motor. Because of that, the compressor won’t be able to start.

Just like the capacitor, a starter relay once defective, you will need to make a replacement.

5. Bad Wiring

Bad wire connectors, corroded, broken, and melted wires could be the reason your compressor is not turning on. Check that the low voltage wires especially from your thermostat are in place and without issues.

Sometimes rodents could create nests inside your compressor housing. If they find their way into your compressor housing, they can chew wires and cause problems with starting your condenser unit.

Final Thought

We hope you have enjoyed this article in finding solutions to a home ac compressor not turning on. We also recommend that you should have regular scheduled HVAC maintenance. You can have HVAC tune ups twice a year, in the spring and fall.

Regular maintenance ensures that your system remains working efficiently, saving you energy.

Regular maintenance can also prevent unforeseen HVAC breakdowns which could be costly. Thanks for reading.

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