Did your AC unit fail to turn on?
It could be due to a bad AC contactor.
The AC contactor is responsible for switching the power to your AC condensing unit on and off.
If the AC contactor stops working, then your AC won’t cool your home.
In this article, I’ll go over all the symptoms of a bad AC contactor. I’ll also cover what you should do if your AC contactor has failed.
The Symptoms of a Bad AC Contactor
If you suspect that you have a bad AC contactor, there are a few symptoms that you should look out for:
- Humming or Buzzing Noise Coming From Your AC Contactor
- Chattering Noise Coming From Your AC Contactor
- Pitting or Excessive Charring on Contacts
- AC Condenser Unit Doesn’t Turn On
I’ll go over them below.
1. Humming or Buzzing Noise Coming From Your AC Contactor
If your AC contactor is making a humming or buzzing noise, then it’s most likely going bad.
Contactors make a buzzing noise when their coils get weak or dirty.
The buzzing noise happens because the contactor’s magnetic coil doesn’t have enough strength to keep the contacts closed. The contactor coil makes a buzzing sound as it tries to stay closed.
Here is a video that shows what it sounds like when your AC contactor is humming or buzzing:
If your AC contactor is making a buzzing noise, then you should swap out your contactor for a new one.
In theory, you can sometimes clean the contactor coil to stop the buzzing and fix the contactor, but it’s usually not worth it since most contactors are not made the be opened up and worked on.
Fortunately, a contactor for an AC unit is fairly inexpensive and simple to replace.
2. Chattering Noise Coming From Your AC Contactor
If your AC contactor is chattering, it might have gone bad.
A chattering noise occurs when your AC contactor rapidly engages and disengages.
AC contactors chatter because of a weak coil or bad electrical connection.
Some contactors chatter when they get old and their coil starts to wear out from heat.
Here is a video that shows what it sounds like when an AC contactor chatters:
If your AC contactor is chattering, you should turn off your AC and check for loose wires at the contactor. Sometimes a chattering contactor is simply caused by a loose wire.
If all the wires are snug and making a good connection, check the voltage at the contactor coil input terminals:
- If you get a constant 24~28 volts AC, then the contactor needs to be replaced.
- If the voltage dips down repeatedly when the contactor chatters, then there could be another component that’s gone bad in your AC – such as a pressure switch.
3. Pitting or Excessive Charring on Contacts
Pitting and charring on the contacts themselves will cause your AC to fail to turn on.
Pitting and charring prevent your AC contactor from forming an electrical connection and will prevent your AC from turning on.
Here is a video that shows what it looks like when a contactor’s contact is pitted:
If your AC contactor is pitted or charred, then you should replace the contactor to get it working properly again.
Some folks will say that you can clean the contacts, but it usually isn’t worth it since contact cleaners will only remove the black residue from the contacts and won’t repair the pitting damage.
4. AC Condenser Unit Doesn’t Turn On
One of the most obvious symptoms of a bad AC contactor is an AC unit that simply doesn’t turn on at all – or keeps turning off while it’s running.
If you find that your AC contactor coil is getting voltage, but the contactor isn’t pulling in, then there’s a good chance that the contactor is bad.
However, a bad AC contactor isn’t the only thing that causes an AC condenser to keep turning off, so you should also check other components such as the air filter, condenser coil, and capacitor.