Abnormal noises from your heating and cooling system are warning signals of imminent mechanical or electrical breakdown. Ignoring these sounds can turn a minor $180 repair into a $4,500 complete compressor replacement.
High-Pitched Screeching or Whistling
A screeching sound coming from the outdoor unit usually indicates high internal pressure buildup within the hermetic compressor dome or unlubricated bearings in the condenser fan motor. High pressure is a safety hazard—turn off the system immediately.
Heavy Metal-on-Metal Grinding
Grinding sounds signify seizes bearings or damaged internal scrolls inside the compressor. If heard from the indoor air handler, the blower wheel fan blade has come loose from the motor shaft and is hitting the metal housing.
Loud Electrical Buzzing or Humming
A low or loud 60Hz humming sound where the outdoor unit fails to turn on is a classic symptom of a bad capacitor attempting to energize a locked motor rotor (LRA). If left energized, the compressor thermal overload switch will trip, or the motor windings will melt.