Compressor loud / rattling / knocking

Compressor

AirCompDX - Field Reference for Air Compressor Techs
All HVAC symptoms
1

Slugging (liquid refrigerant returning)

high
CheckCold, sweating suction line all the way to compressor; low superheat.
FixCorrect overcharge, verify TXV bulb strapped and insulated, check for defrost stuck in cool mode.
2

Broken mounting grommets / loose panels

low
CheckPanels vibrate; compressor tilted.
FixReplace rubber isolator grommets; tighten fasteners.
3

Failed internal valves (recip)

critical
CheckHigh suction, low head, low amps.
FixCompressor replacement.
Safety

Pull the disconnect and lock out before opening HVAC equipment. Discharge dual-run capacitors before handling. Refrigerant recovery and brazing require EPA 608 certification and proper PPE.