The condensing unit or outside portion of a central air conditioner contains a motorized blower fan that plays a vital role in the system's operation. The fan doesn't actually provide any of the air you feel inside your home but rather helps nearby parts continue to operate properly without overheating and triggering the system's safety shut down.

What does the fan do and what potential problems with the fan can cause the system to shut off unexpectedly?

Condenser Fan Function

The condenser fan points at the condenser coils, which receive gas refrigerant from the compressor that then turns the gas into a liquid for easy transport inside the house to the air handler portion of the unit. The coils become warm during the phase change but the calibration of the coils and the presence of the fan, which blows ambient air over the coils, are both meant to prevent the coils from overheating.

If your system starts throwing an overheating warning and shutting down, those coils are likely overheating for some reason. Check to make sure the coils are clean, as dirt can cause the coils to overheat even with the fan. But if the coils are clean, the problem is likely in the condenser fan.

Potential Problem: Bent or Loosened Blades

The fan's blades can become bent or loosened from the motor shaft and both of those problems can cause a fan slowdown that can allow the coils to overheat. You can check on the health of the blades by turning off the power to your condensing unit, removing the fasteners on the grated fan cover on top of the unit, and then lifting straight up on the unit. Flip the whole piece over so the grate is at the bottom and you will now be looking at the fan blades on top.

Conduct a visual inspection to see if any blades look bent or broken and, if so, call in an air conditioning repair service to replace the blades. If the blades look in good condition, conduct a spin test.

Simply push the blades around the motor shaft for a couple of rotations checking for looseness or wobbling. If the blades wobble, you need to tighten the set screw in the middle. Test the blades again to make sure it is tight enough.

Potential Problem: Broken Fan Motor

Instead of feeling looseness during the fan test, do you feel a firm pressure that makes it difficult to turn the blades at times? This hints towards a broken fan motor that is starting to impair your fan's functionality and will eventually cause the fan to stop working altogether.

Call in an HVAC company like One Hour Heating & Air Conditioning to replace the motor before you try to operate the unit again.