AC Compressor Problems and Repair Options

What the Compressor Does

The compressor raises the pressure and temperature of refrigerant vapor so it can release heat at the outdoor coil. Without it, refrigerant does not circulate and the system cannot cool, even if the fans run normally and the thermostat operates perfectly.

Compressors are built to run for years, but they are vulnerable to a specific set of stresses: liquid refrigerant returning to the suction line, operating with low charge, high head pressure from a dirty coil or restricted airflow, electrical supply problems and lubrication failure.

Symptoms Homeowners Notice

• The outdoor unit hums loudly but nothing starts
• A hard clunk or shudder each time the system tries to start
• The breaker trips whenever the system calls for cooling
• Cooling has become weak while the outdoor fan runs normally
• The compressor runs for a few minutes, then shuts off on protection
• New grinding, rattling or metallic noises from the outdoor cabinet

What a Technician Evaluates

The purpose is to distinguish a compressor that has genuinely failed from a compressor that is being prevented from starting by a cheaper component. That distinction is worth thousands of dollars, and it is a reasonable thing for a homeowner to ask about directly.

• Voltage supply and electrical connections at the disconnect and contactor
• Capacitor capacitance and start components
• Compressor winding resistance and ground faults
• Amp draw against rated load amps
• System pressures, superheat and subcooling
• Condenser coil cleanliness and airflow across it
• Evidence of refrigerant leakage or contamination

Repair, Replace the Compressor, or Replace the System

If the compressor itself has failed, three paths generally exist. On equipment still under manufacturer warranty, compressor replacement may be substantially less expensive because the part is covered, though labor and refrigerant usually are not. On out-of-warranty equipment, compressor replacement is a major labor and materials investment in a machine whose remaining components are the same age.

For older systems — particularly those using R-22 or already carrying a history of repairs — the total cost of a compressor replacement often approaches a meaningful share of a new system, and many homeowners weigh full replacement instead. Our calculator helps organize that comparison, and the repair-or-replace guide covers the factors in detail.

Whichever path you choose, ask what caused the failure. Installing a new compressor into a system with an unresolved leak, a restricted metering device or a dirty coil sets up the same failure again.