Compressor Failure: The Expensive One, and What Causes It
Compressors rarely fail on their own. Almost every failure we see was caused by something upstream that went unaddressed.
Air conditioning compressors typically fail from causes other than age: liquid refrigerant returning to the compressor, running with low refrigerant charge, electrical problems including a failing capacitor forcing repeated hard starts, restricted airflow, and overheating from a dirty condenser coil. On systems past ten years, compressor replacement usually argues for full replacement.
What a compressor does
The compressor is the pump at the center of the refrigeration cycle. It takes low-pressure refrigerant vapor from the evaporator and compresses it into high-pressure vapor, which then releases its heat in the condenser.
It is the single most expensive component in the system, and in most residential equipment it is a hermetically sealed unit — motor and pump in one welded shell. It cannot be opened or rebuilt in the field.
When it fails, the options are replacement of the compressor or replacement of the system, and on most Valley equipment the second one is the better decision.
Why compressors fail
| Cause | Mechanism |
|---|---|
| Liquid slugging | Liquid refrigerant reaches the compressor; liquid does not compress |
| Low charge | Refrigerant also cools the motor windings; low charge means overheating |
| Failing capacitor | Repeated locked-rotor starts heat and degrade winding insulation |
| Dirty condenser coil | Head pressure and current rise, running the compressor hot continuously |
| Restricted airflow indoors | Causes coil freezing, which causes liquid return |
| Acid formation | Moisture in the system from poor evacuation forms acids that attack windings |
| Voltage problems | Brownouts, surges, and loose connections |
| Overcharge | Excess refrigerant floods back to the compressor |
Notice what is not on that list: normal age. Compressors in properly maintained systems typically outlast the rest of the equipment. Nearly every failure we see has an upstream cause.
The capacitor connection
This is the one worth understanding, because it is the most preventable.
When a run capacitor degrades, it cannot deliver adequate starting torque. The compressor attempts to start and draws locked-rotor current — many times normal running current — repeatedly.
That current heats the motor windings. Repeated over days or weeks, it degrades the insulation on those windings. Eventually they short, and the compressor is finished.
A capacitor is an inexpensive part with a measurable degradation curve. Testing it at spring maintenance and replacing it when it reads low is the single most effective compressor protection available, and it is why we measure microfarads rather than just checking whether the system runs.
Signs of a failing compressor
- The system runs but cooling is weak, with a temperature split well below normal
- The breaker trips when the system attempts to start
- A loud hum from the outdoor unit with no compressor start
- Grinding or rattling from inside the compressor shell
- The compressor cycling on its internal overload — running briefly, then stopping, then restarting after a cool-down period
- Refrigerant pressures that do not differentiate properly between the high and low sides
The replacement decision
Compressor replacement is labor-intensive: recover refrigerant, cut out the old compressor, install and braze in the new one, replace the filter drier, pull a deep vacuum, and weigh in a full charge.
On a system under eight years old, the compressor may be under manufacturer parts warranty — which covers the part but typically not the labor. That still makes replacement of the compressor the right call.
Past ten years and out of warranty, the cost usually approaches enough of a replacement system that it is hard to justify. You are making a significant investment in equipment with limited remaining life, and the rest of the system has aged alongside the compressor.
On an R-22 system, it is not a close question.
If the compressor burned out
A burned-out compressor motor contaminates the entire refrigerant circuit with acid and debris. Replacing the compressor without thoroughly addressing that contamination guarantees the new one fails too.
A proper burnout cleanup means replacing the filter drier — often with a suction-line drier as well — flushing the line set, and in some cases replacing the line set entirely. That work adds cost and time.
It is also a reason replacement often makes more sense: a full system replacement includes a new indoor coil and properly handled line set, which sidesteps the contamination question entirely.
Frequently asked
How much does it cost to replace an A/C compressor?
It is the most expensive single component repair on a residential system, and on equipment past ten years the cost typically approaches enough of a replacement system that replacement is the better decision. Under warranty, the part may be covered but the labor usually is not.
What causes an air conditioner compressor to fail?
Rarely age. The common causes are liquid refrigerant returning to the compressor, running with low charge, a failing capacitor forcing repeated hard starts, a dirty condenser coil causing chronic overheating, and moisture in the system forming acids.
Is it worth replacing a compressor?
Under eight years and possibly under warranty, yes. Past ten years and out of warranty, usually not — the cost approaches replacement, and the rest of the system has aged alongside the compressor. On an R-22 system, replacement is clearly the better decision.