Compressor

What the compressor does and why it fails

Sitting inside the outdoor unit, the compressor draws in cool, low-pressure refrigerant vapor from the indoor coil and compresses it into hot, high-pressure vapor. That pressure difference is what drives refrigerant around the loop and what allows the system to dump indoor heat into hot summer air. Most residential systems use scroll or rotary compressors; newer variable-speed (inverter) compressors adjust output to match the load instead of running at one fixed speed.

Compressors rarely fail without a cause. Common culprits include low refrigerant from a leak (which starves the compressor of the cool vapor that also cools its motor), liquid refrigerant slugging back from a flooded coil, electrical problems like failing capacitors or contactors, dirty coils that drive pressures too high, and chronic short cycling. Many sudden "compressor failures" are actually the end stage of a smaller problem that went unaddressed.

Repair or replace when a compressor dies

Because the compressor is the costliest part in the system, its failure forces a real decision for Southeastern PA homeowners. On a newer system still under parts warranty, replacing the compressor usually makes sense. On a system that is well into its service life — or one using phased-out refrigerant — putting a major component into a tired unit often costs more in the long run than replacing the system. Soft signs of compressor trouble include hard starting (lights dimming at startup), growling or clattering from the outdoor unit, and breakers tripping. Annual maintenance that keeps coils clean and verifies charge and electrical components is the cheapest insurance a compressor can get.