A central air conditioner's condenser unit is the part of the system that's outside your house. This is where the cooling process starts once the unit receives a signal from your thermostat. A compressor pumps out gas refrigerant into condenser coils, which change the gas into a liquid in a process that makes the surface of the coils hot. A nearby condenser fan blows onto the coils to prevent overheating to make sure the system doesn't shut down and there's no issues with the refrigerant phase change.
If your condenser fan malfunctions, your air conditioner can become less efficient, shut down unexpectedly, or stop working completely. You might stand next to the condenser unit while it runs and notice that it doesn't sound as if the fan is operating normally. The sound the fan makes can help determine the cause and help steer you and your heating and air conditioning technician in the direction of a solution.
Start-Stall Fan Sound: Broken Capacitor
Does the fan start up normally but quickly shut back down? There could be a problem with the run capacitor that provides an electrical boost to keep the compressor working properly. If the run capacitor is on the fritz, the compressor can shut off prematurely and shut off the system.
You can check the run capacitor yourself if you own an insulated screwdriver and a multi-meter that includes Ohms readings. Make sure the power to the air conditioner is completely turned off, and then open the access panel door and locate the capacitor.
Unhook the wires attached to the terminals then place the insulated screwdriver over the terminals for several seconds until the capacitor is drained of its stored electrical charge. You can then hook up the multi-meter probes to the terminals, wait for the reading, and make sure the reading matches the Ohms range printed on the side of the capacitor.
Squeaking or Rattling Sound: Loose Fan Blades
Does the fan make a squeaking or rattling sound as it spins around in the condensing unit? The fan blade assembly might have come loose from the motor and the noise you hear is the assembly wobbling as it spins. A loosened blade assembly can make the fan put out less air and cause overheating and inefficient refrigerant transfer.
You can check the fan blades yourself by turning off the power to the unit, removing the mounting screws from the grated domed cover on top of the unit, and then lifting that dome straight up before flipping it over. The fan blade assembly should now be facing you.
Examine the blades for any obvious signs of damage or looseness. Try to spin the blades around in a circle with your hand. If you experience no wobbling but do have resistance, there might be a problem with the motor. If the fan blades wobble, simply tighten the retaining nut with a wrench and put the unit back together.
You shouldn't try to fix damaged blades that could cause the same sound. Call an air conditioning repair service for a new blade assembly instead.