Before condemning a compressor, technicians must perform three critical electrical tests using a calibrated digital multimeter at the compressor terminal pins (Common, Start, and Run):

• Winding Resistance Test (C-S-R relationship): For single-phase compressors, the resistance from Start to Run (S-R) must equal the sum of Common to Start (C-S) and Common to Run (C-R). If any reading is open (infinite resistance), the winding is broken. If resistance is zero, a short circuit exists.
• Ground Fault Test: Measure resistance from each terminal pin to a clean copper ground source. Any reading other than infinite resistance (O.L.) indicates a grounded winding, meaning the electrical insulation has failed and the compressor must be replaced.
• Megohmmeter Testing (Megger): For commercial compressors, a standard multimeter is insufficient to detect early insulation degradation. A megohmmeter applying 500V or 1,000V DC must be used; a reading below 20 Megohms indicates severely degraded winding insulation.

If a compressor fails due to an electrical burnout, the extreme heat decomposes the refrigerant and oil, creating highly corrosive inorganic acids. Installing a new compressor into an acid-contaminated system guarantees premature failure of the replacement unit. Technicians must perform an acid test on the recovered oil. If acid is present, a complete system flush must be performed, a high-capacity suction line filter dryer must be installed to protect the new compressor, and the liquid line filter dryer must be replaced. The suction dryer should be monitored and replaced after 48 hours of operation if pressure drop exceeds manufacturer limits.

Sourcing a replacement compressor requires precise specification matching. Technicians must document the model number, serial number, electrical characteristics (voltage, phase, Hz), refrigerant type, oil type (POE, Mineral, PVE), and mounting foot dimensions. Copeland compressors are widely used in commercial refrigeration and air conditioning. When cross-referencing compressors, always match the BTU/hr capacity and evaporating temperature range (High, Medium, or Low Back Pressure) rather than relying solely on nominal horsepower ratings.

OEM Compressor Sourcing & Cross-Referencing

Need help cross-referencing a Copeland scroll, Carlyle semi-hermetic, or Tecumseh reciprocating compressor? Contact the HVACProSales engineering support team with your model and serial number.