The industry's rule of thumb is the 50% rule: if a repair costs more than 50% of the price of a new system, replacement is usually the better financial move. It's a starting point, not a full answer — age, efficiency, and repair history matter just as much.
The age threshold
Most AC systems are designed to last 12–15 years. A repair on a unit under 8 years old is usually worth doing. A major repair (compressor, coil) on a system over 12 years old is often better redirected toward a full replacement, since the rest of the system is approaching end-of-life anyway.
The real cost comparison
- Average major AC repair: $500–$2,500 depending on the component (compressors and coils sit at the high end)
- Average full system replacement: $5,000–$12,000+ depending on home size and efficiency tier
- Efficiency gain: A system installed 12+ years ago is often 20–40% less efficient than a current SEER-rated unit — that difference shows up directly on summer utility bills
Repair history is a signal, not noise. A system that's needed two or more significant repairs in the past two years is telling you something the age alone won't — replacement is very likely the better long-term math even if the unit is technically still under the age threshold.
When repair is clearly the right call
- The system is under 8 years old
- This is its first major repair
- The repair cost is under 30% of a full replacement
- The rest of the system (ductwork, thermostat, insulation) is in good condition
When replacement is clearly the right call
- The system is 12+ years old and needs a major component repair
- You've had multiple repairs in the last 24 months
- Your utility bills have climbed noticeably without a clear cause
- The unit still uses R-22 refrigerant (phased out — increasingly expensive and hard to source)
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