Air conditioning units have become commonplace in life, leading you to believe that if it doesn't work and cool properly, you should promptly call a repairman. Some humming noises from air conditioners require a repairman's expertise, however. Do not attempt to work on an air conditioner if you are not experienced with the machine.

A variety of reasons can cause a central air conditioning unit to hum.

Loose Hardware

A humming noise that occurs the whole time the air conditioning unit is running could indicate loose hardware. To check if this is the problem, you should first disconnect the power to the air conditioner, and ensure that each nut and bolt is properly tightened. An additional hint that hardware could be the culprit is listening for small metallic dings every so often, which indicate that the nut is knocking against the bolt. Never attempt to tighten nuts and bolts when the electricity is running to the unit as it could prove dangerous.

Seized Compressor

If the air conditioner is humming but is not emitting cool air, the fan motor or compressor may be seized up, refusing to allow the air conditioner to cool. Although a seized compressor can be temporarily repaired by cleaning it thoroughly, by ensuring that the oil is properly filled and by pushing the motor backwards and forwards, you should not depend on the compressor to last for a long time. This is a temporary fix, and the compressor must be replaced soon. The compressor can be initially damaged by changing the unit directly from cool to heat without turning the unit completely off in between cycles as it puts undue pressure on the compressor.

Fan Is Blowing

The humming sound may be the sound of the air conditioner fan running. When the home becomes exceptionally warm, the fan in the air conditioning unit turns on to remove some of the hot air from the space. Shortly after the fan turns on, the air conditioner should turn on and begin cooling the air. If this is the case, there is no need to call a repairman to have your unit serviced. This also happens in the winter when your central air conditioning unit overheats. If the blowers inside become too warm, the fan will turn on and remove the heated air from the unit. Sometimes it is routed inside the home and other times it is routed outdoors, depending on how your unit is set up.

Needs Cleaning

An air conditioner that hums but doesn't cool the air could also need cleaning. Periodic cleaning should be performed at least once a year to maintain the proper working conditions for the unit. Wipe down the exterior of the air conditioner with warm, soapy water, and work on the inside of the unit. Always ensure that the electricity is disconnected when working with the appliance.