While sitting inside your house, you may have started hearing a faint squealing noise. Upon further investigation, you discovered that the high-pitched sound is coming from your central air conditioner sitting outside. There are a couple of potential causes of this sound, both of which should be taken care of as soon as possible.
Fan Belt Is Stretched or Damaged
One possible reason why your central air conditioning unit has started to make squealing noises could be the fan belt. The belt, located between the motor and fan, rotates around the parts' pulleys.
If the fan becomes stretched or otherwise damaged, it will not be able to keep the proper friction as it travels inside the grooves of the pulleys. As the belt slips, the temporary loosening of it will create the sound until the belt is once again able to grab ahold of the pulleys.
When this happens, two issues may arise. First, the fan will rotate erratically, making it difficult for it to move air through the unit.
Second, the belt will become more stretched or damaged if it is not changed. Eventually, the belt will break and the fan will not turn. Before this happens, have the belt replaced by a professional. They can also check to make sure there is nothing wrong with the pulleys that may have lead to the issue.
Bearings Inside the Motor Are Worn
Another possible cause of the squealing sounds is that the bearings inside of the A/C unit's motor have become worn. Normally, these bearings are surrounding by a lubricant that allows them to move freely against each other.
However, if the lubricant runs dry or the bearings are just old and worn down, the metal surfaces will rub against each other. This rubbing will create the sound you are hearing as well as produce friction and heat that will cause further wear on the bearings.
Eventually, this will cause the motor to burn up, requiring that you either replace the motor or the entire A/C unit. It is better to have the bearings inspected as soon as you hear the noise.
When you start hearing squealing noises coming from your home's central A/C unit, you need to have it fixed before the underlying cause gets worse. Contact an air conditioning repair service to have them send a technician to diagnose the issue and take the necessary steps to fix the problem.