Compressor HVAC: Testing and Inspection

A faulty compressor will display one or more of the following symptoms: noise, seizure, leakage or low inlet and discharge pressure. A steady, resonant noise from the compressor is not necessarily an indication of a problem, but irregular metallic rattling may indicate broken parts and should be investigated. A thumping noise from the compressor and a cool, sweating suction line into it may indicate an overcharged system. Check seizure by disengaging the magnetic clutch and rotating the driven plate. If the compressor is seized, the driven plate will not rotate.
False compressor seizure may occur after an extended period of disuse or storage. Lubricating oil drains away from the polished surfaces of ball seats and axial plate and the compressor appears to be seized. Use a clutch hub holding tool to turn the compressor in the opposite direction of rotation at least three revolutions. Check for false compressor seizure if compressor has not been used in a month or longer.
If compressor is not seized but will not rotate, check for current at magnetic coil. Low discharge pressure may be caused by faulty seals within the compressor, a restriction in the compressor or elsewhere, or by a low refrigerant charge. The compressor must have the correct amount of the proper viscosity oil. Excess oil will restrict refrigerant circulation and reduce compressor outlet pressure.