Air conditioners vary widely in the level of noise they produce. Should you find your unit to produce noise at an unusually high volume or in irregular patterns, you may have a problem with the compressor. Should you determine the noises to be coming from your air conditioner compressor, there are several possible compressor-related explanations which range from minor to serious malfunctions.
Before having the air conditioner compressor inspected, be sure to determine that the noise level is not simply part of functional operation. Though this may seem to be common sense, many people do not realize the degree of noise their air conditioner produces when running smoothly. If you have recently begun living with the unit or if you are unaccustomed to using an older unit, you may simply own a noisy air conditioner. Also be sure to determine whether the sound is coming from the compressor or from other elements such as the air ducts or air handler, both common sources of AC noise.
Loosened or stray hardware
Does the AC noise sound like metal clattering? Loose hardware is one common problem in compressors. This is a simple problem to determine, though it is still recommended to hire a HVAC professional to open and inspect the compressor unit. When looking for loose hardware, check the refrigerant tubing, noting whether it is bent too closely to another element. It is also possible that a screw or a needless piece of material was dropped into the unit during shipping, which may cause the rattling.
A “floodback” of refrigerant
Is the noise only noticeable as the compressor starts up? This could point to a problem of refrigerant floodback. In this scenario, the refrigerant is literally flooding into the crankcase of the compressor. If you suspect your compressor is experiencing floodback, be sure to have an HVAC technician inspect the unit at the moment that the compressor is starting up. The problem may be solved at relatively little expense by installing a new crankcase heater.
Do you have an older air conditioner? Though it is unlikely in most modern units, there is always some possibility of an oil leak within the compressor unit. You may make a preliminary inspection on your own, without needing to open the compressor. Look for evidence of oil leakage outside and around the compressor. Should you find oil leakage, the resulting low level of oil could easily be causing the noise. If your unit happens to have an oil gauge, check that it reads between 1/2 and 3/4 full. Anything above or below this range can cause noise and will warrant calling in a professional for a refill.
Would you describe the compressor noise as a loud humming? Humming or thrumming noises can point to a problem with the starting capacitator. Note how the motor is functioning, whether it takes a while to start, or in fact never starts at all. In either case, this can indicate trouble with the starting capacitator. You might solve the problem with a "hard start kit", a product specially designed to jump-start capacitators and compressors having this problem.