AC Repair or Replace? A Decision Framework With Real Numbers

Published 2026-09-11

The call that ends every summer: the air conditioner quits, the technician quotes a repair, and somewhere in the conversation the words "you might want to think about replacing it" come up. Sometimes that is salesmanship. Often it is arithmetic. This framework separates the two using three numbers you can get in an afternoon.

The three numbers

• The unit's age against its design life. Central air conditioners and heat pumps are built for roughly 12–15 years in most of the country, less in hot-humid and desert metros where the compressor runs eight or nine months a year. Gas furnaces run 15–20 years; electric furnaces longer. Past about 80% of design life, a repair buys months, not years.
• The repair quote. Localized ranges for common fixes, compressor replacement, and furnace repair are in our HVAC cost tables — for Houston, Nashville, Denver, and 30 other metros.
• Full replacement cost, locally. Same tables: the central AC replacement, furnace replacement, and heat pump rows. That figure is the denominator.

The one-third rule (and the $5,000 rule)

The heuristic contractors use most: if the repair quote is more than about a third of local replacement cost on a unit past mid-life, replace. A repair does not reset the clock on the parts that were not replaced; on an old system the next failure is already on the schedule.

You will also hear the older "$5,000 rule" — multiply the unit's age by the repair cost and replace if the product exceeds $5,000. It was coined when equipment was cheaper, and it now points toward replacement too early. Use it as a tiebreaker, not a verdict.

Repairs that end the conversation

Some findings settle the question by themselves:

• A cracked heat exchanger in a gas furnace. Carbon monoxide risk; the part costs nearly as much as a furnace and the labor is heavy. Replace.
• A failed compressor out of warranty on a unit past ten years. The compressor is the single most expensive part — the cost tables show it landing at a quarter to half of a new system — and the rest of the unit has the same mileage.
• A refrigerant leak on an R-22 system. R-22 has not been produced since 2020; a recharge is a loan against a dwindling supply at rising prices. See why new AC quotes jumped in 2025 for the current refrigerant picture.
• A second major repair in two seasons. Two failures are a pattern.

Modifiers that tilt the decision

Toward replacement:

• The unit is oversized or undersized and rooms never hold temperature; a properly sized replacement fixes comfort that no repair can.
• Efficiency. Today's minimum-efficiency unit uses roughly a third less cooling energy than a 2005-era 10 SEER unit. Savings alone rarely justify replacing a working system, but they lower the effective cost of one you are replacing anyway.
• Matched-system rules. Manufacturers want the indoor coil and outdoor unit matched; swapping only the condenser onto an old coil can void coverage and lose efficiency. That makes a "just the outdoor unit" option less attractive than it sounds.
• Timing. Replacements quoted during a July heat wave cost more and leave fewer equipment choices. If you can limp to shoulder season, bids improve.

Toward repair:

• The unit is under ten years old with a single failed part and a clear cause (capacitor, contactor, fan motor, drain line).
• Parts are still under manufacturer coverage — most brands cover parts for five years, ten if the unit was registered; labor is usually yours after year one.
• Cash flow cannot absorb a four- or five-figure replacement; an honest repair plus a savings plan beats a rushed decision.

Running your own math

Take central AC (or furnace) replacement for your metro from the HVAC index and multiply by 0.33. Hold every repair quote against that line. Example shape, using your local table rather than these numbers: if replacement in your metro runs $6,200 typical and the fan-motor repair is $450, repair without a second thought. If a compressor quote is $2,400 on a 13-year-old unit, you have crossed the line; collect replacement bids, insist on a load calculation (Manual J) rather than a rule-of-thumb tonnage, and get at least three.

Also check whether insurance covers any of it — usually not, but lightning and hail are the exceptions.

The unit does not care what you have already spent on it, and neither should the math.

Cost data