Repair or Replace: When an Old AC Is Not Worth Fixing

Repair an old AC when one bounded part has failed and the rest of the system is sound. Replace it when the unit is well past its working life, keeps breaking, leaks refrigerant from the coil or can no longer keep the house comfortable. The fix that costs less and lasts is the right one.

How old is too old to repair an AC?

Age sets the question, not the answer. ENERGY STAR says a heat pump or air conditioner more than 10 years old is worth a professional evaluation. Contractor sources commonly put the working life of residential cooling equipment at 15 to 20 years with routine maintenance.

So a unit at 10 to 12 years is a candidate for a check, not a funeral. A unit at 18 with a corroded coil and a compressor that hums on startup is a different case.

What does the repair history tell you?

Count the repairs and the time between them. ENERGY STAR's warning signs are frequent repairs combined with rising energy bills, rooms that are too hot or cold, humidity problems and noise. One of those is a nuisance. Three together mean the system is losing ground.

A rule of thumb many contractors use: if a single repair costs about half of a replacement, and the unit is past 10 years old, replacement deserves a serious look. It is a prompt for a discussion, not a law. Ask for both numbers in writing so you can see them.

A worked example: cost per year of life

Compare what each choice costs per year of use you can reasonably expect. These numbers are illustrative arithmetic, not a quote.

The fan motor repair wins because it is cheap against the life it buys. The coil repair loses, because a 17-year-old unit has little life left to buy and the next failure is likely. Ask the technician honestly how many years the repair should buy, then do this arithmetic with your own quote.

Before you approve a repair on an older unit, ask four things:

1. What failed, and what else on the unit is near the same condition?
2. Is the refrigerant charge correct, and is there a leak?
3. How many years should this repair reasonably buy?
4. What would replacement cost, in writing, for the same scope?

Does R-22 or R-410A change the decision?

It can. R-22 production and import ended on January 1, 2020, per the EPA. The EPA also says reclaimed and stockpiled R-22 should meet owners' needs well past the phaseout date, and that homeowners are not required to replace an R-22 system. So a capacitor or fan motor repair on an R-22 unit still makes sense. A large refrigerant leak on one is the case where cost and supply start to push toward replacement.

R-410A systems can be serviced as usual. The EPA's May 2026 revision removed the installation deadline for R-410A equipment manufactured or imported before the cutoff, according to ACHR News. New residential split systems built since January 1, 2025 use lower-GWP refrigerants, usually R-454B or R-32.

From the field: when replacement was the honest answer

We would rather fix than sell, but the reviews show both outcomes. One Google reviewer, Ms. O., described an air conditioner that was leaking lots of water, rusty and so old and damaged that the house would not reach the right temperature. The system needed replacement, a new one was installed and the home was back to normal.

Another reviewer, Margaret S., found that a prior repair had not included the capacitor it was supposed to. That is the other side of the coin: before you buy a new unit because of a repeat failure, confirm the earlier repair was real. A recurring fault often means the first diagnosis missed the cause.

What does replacement cost in the St. Louis area?

Angi reports that a full HVAC replacement in St. Louis runs $4,755 to $11,888 in 2026, averaging $7,133, with labor at $75 to $150 per hour. An AC-only replacement costs less than a full system, and an older furnace or damaged ductwork can add to it.

ENERGY STAR notes that a new AC connected to an old furnace blower will not perform to its rating, and that replacing both is especially worth considering when the furnace is over 15 years old. The federal minimum for a split AC in Missouri's region is 13.4 SEER2, according to the Department of Energy. Do not budget for the federal 25C tax credit, which the IRS says does not apply to property placed in service after December 31, 2025.

Replace only the outdoor unit, or the whole system?

The EPA's refrigerant FAQ says a broken condensing unit can be replaced if the new one meets regional efficiency standards. That is the cheaper path, and it has limits.

Do not accept a match that the installer cannot document by model number.

How should you size and compare a replacement?

Insist on a load calculation. The old unit's tonnage is not a design, and many older homes have been renovated, re-insulated or had windows replaced since it was installed. Our AC installation page explains what a proper sizing visit includes.

Compare quotes by equipment model, efficiency rating, scope of work, who pulls the permit, removal of the old unit and payment terms. Our guide to choosing an HVAC contractor lists the checks. South county subdivisions around Mehlville and Lemay have many older split systems where this decision comes up every summer.

When is the best time to replace?

Before the failure, if you can choose. St. Louis recorded 49 days at or above 90°F in 2025, according to the National Weather Service, and a unit that quits in July leaves you comparing quotes in a hot house. In spring or fall you can collect two or three itemized quotes, check license numbers and ask about the permit without the pressure. If the AC is still running but you are watching it age, a spring tune-up shows whether it will last the summer.

A replacement is permit work in the City of St. Louis and in St. Louis County, so ask each contractor who pulls the permit and get the answer in the quote.

Next steps before you call

Get the unit's age and refrigerant type from the data plate, write down the last two repairs, and call. We diagnose first, explain the problem in plain language and give you options. Our AC replacement and AC repair pages show both paths. We are open 24 hours. Same-day service is possible when the schedule allows.