This decision usually gets made under pressure, in July, by whoever is standing in front of you with a quote. Working through it beforehand is worth more than any negotiating tactic.
Three things decide it: age, refrigerant type, and the repair cost as a share of a new system. Any one of them can settle it alone. A system past fifteen years, running R-22, needing a compressor is not a repair decision — it is a replacement wearing a repair quote.
Start with age
Typical central air systems last somewhere in the region of fifteen to twenty years, with maintenance and climate moving that considerably in both directions.
Under 10 years — repair, almost always. The system has most of its life ahead and modern efficiency gains will not repay a replacement yet.
10 to 15 years — genuinely the judgement zone. A small repair is fine. A large one deserves the arithmetic below.
Over 15 years — the balance tips hard toward replacement. Not because it will fail tomorrow, but because every repair is now buying a short extension on equipment that is behind on efficiency and getting harder to source parts for.
Then check the refrigerant
This one detail changes the decision more than most people expect, and it applies to a large number of systems still running.
Older air conditioners use R-22. Its production and import has been phased out in the US under the ozone-protection rules, so servicing one now depends on reclaimed refrigerant — a shrinking supply at rising prices.
The practical effect: a refrigerant leak in an R-22 system is not a routine repair. You are paying premium prices to refill a system that will leak again, on a substance that gets scarcer each year.
If your system uses R-22 and has a refrigerant leak, that alone usually justifies replacement. Your technician can tell you which refrigerant you have in seconds, and it should be the first question you ask.
A widely repeated heuristic multiplies the system's age in years by the repair cost, and suggests replacing when the result passes a few thousand dollars. A fifteen-year-old unit needing a $400 repair scores 6,000; a five-year-old unit needing the same scores 2,000.
It is a reasonable first read and it is not arithmetic. It ignores your electricity rate, your climate, how long you plan to stay, and whether the rest of the system is sound. Use it to sort obvious cases quickly, then think about the ones it puts near the line — do not let it make the decision.
The repairs that usually mean replacement
Compressor failure on an older system. It is the most expensive single component, so replacing one in a fifteen-year-old unit spends a large share of a new system's cost on equipment that is already old.
Evaporator or condenser coil replacement, similarly — a major part, major labour, on ageing equipment.
Repeated refrigerant leaks. Refrigerant is not consumed in normal operation. If it needs topping up, it is leaking, and repeated top-ups treat the symptom while the leak continues.
Anything on an R-22 system involving the sealed refrigerant circuit.
The repairs that are usually worth doing
Capacitors, contactors, fan motors, thermostats, condensate pumps, control boards. These are ordinary wear items — comparatively inexpensive, and their failure says nothing about the rest of the system.
A ten-year-old unit with a failed capacitor is a ten-year-old unit with a failed capacitor. Replace the part.
What to ask before you decide
- Which refrigerant does it use? The single most decision-relevant fact.
- What exactly failed, and why? A part that failed from age is different from one that failed because the system was oversized and short-cycling.
- What else is close to failing? An honest technician will tell you.
- How long do I plan to stay in this house? Efficiency savings need years to accumulate.
- What is the repair as a share of replacement? Above roughly a third, on an old system, replacement usually wins.
One thing worth checking first
Before accepting either quote, confirm the problem is the equipment. Restricted airflow from a blocked filter, closed vents or leaking ducts produces symptoms that resemble a failing system — poor cooling, long run times, freezing coils — and gets misdiagnosed regularly.
A filter costs almost nothing to rule out, and duct leakage is worth assessing whatever you decide, because it undermines a new system exactly as much as an old one.
If replacement is the answer, the next question is what type — see heat pump vs central air.
This is general information, not professional advice — see our disclaimer.
Frequently asked questions
At what age is replacing usually better?
Once a system is past roughly fifteen years, the balance tips quickly. Parts get scarcer, efficiency is well behind current equipment, and any large repair buys only a short extension.
What is the R-22 problem?
Older systems use R-22 refrigerant, whose production and import has been phased out in the US. Recharging one now relies on reclaimed stock, which is expensive and getting more so.
Is there a rule of thumb?
A common one multiplies the unit's age by the repair cost and suggests replacing if the result exceeds a few thousand dollars. It is a heuristic, not arithmetic — useful for a first read, not a decision.
Does a compressor failure mean replacement?
Usually, on an older unit. The compressor is the single most expensive component, so replacing one in a fifteen-year-old system means spending a large share of a new system's price on old equipment.
Will a new system actually cut my bills?
If the old one is genuinely old, yes — minimum efficiency standards have risen substantially. How much depends on your climate, rates and how the new system is sized and installed.
Sources
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