Short answerRepair the air conditioner when it is under 12 years old, uses R-410A, and the failed part is a capacitor, contactor, fan motor or minor leak. Lean toward replacement when it is 13-plus years old, runs on R-22, needs a compressor or evaporator coil, or the repair would cost more than about a third of a new system. In Southeast Michigan the compressor and R-22 questions settle most cases.
The question is really three questions
Homeowners ask "should I fix it or replace it" as if there were one answer, but the decision breaks into three separate things: how old the system is and what refrigerant it uses, which part actually failed, and what the new system would save you. Put honest numbers on each and the answer usually becomes obvious. Our reputation in Ypsilanti and Ann Arbor is built partly on telling people not to replace, so we will walk through this the way we do at a kitchen table.
Question one: age and refrigerant
A split-system central air conditioner in Southeast Michigan lasts 15 to 20 years when it is maintained and sized right, less when it sat in a south-facing bed of mulch with a coil that was never cleaned. The run hours here are modest, about 600 to 900 a year, which is why we see 1999 condensers still working in Plymouth Township. But age alone is not the deciding factor. Refrigerant is.
If your outdoor unit was installed before 2010, it almost certainly runs on R-22. Production of R-22 ended in 2020 and the remaining supply is reclaimed gas at a price that climbs each year. A system that needs a pound or two after a leak repair is still fixable; one that needs a full charge after a coil or compressor replacement is getting a very expensive repair on a system that is by definition at least 15 years old. R-22 refrigerant phase-out in Michigan explains the market in detail.
Systems from 2010 to 2024 run on R-410A, which is widely available and reasonably priced, and parts for them are everywhere. New equipment since 2025 uses R-454B or R-32 under the federal refrigerant transition, which does not affect your existing R-410A system but does mean a new condenser cannot be matched to an old R-410A indoor coil. A replacement is a full system, condenser and coil together.
Question two: which part failed
The part matters more than the age.
- Capacitor, contactor, fan motor, thermostat, float switch, Schrader valve leak. Repair, on almost any system that is not already leaking refrigerant elsewhere. These are inexpensive, same-day fixes, and they do not signal that the rest of the system is tired. See AC capacitor failure signs for the most common one.
- Condenser fan motor on a 15-year-old unit. Still usually repair, but it is a flag; the compressor has seen the same 15 years.
- Refrigerant leak in the evaporator coil. The coil is the second most expensive part. On a system under 10 years, a coil replacement under parts warranty is reasonable. On an R-22 system, a new coil plus a charge of reclaimed R-22 rarely makes sense.
- Compressor. This is the decision point. A compressor is roughly half the cost of a new condenser once labor and refrigerant are included. On a system under 8 years with a parts warranty, replace the compressor. On anything older, and on any R-22 system, replacement of the whole system almost always wins.
- Leaking line set in a slab or wall. A line set buried in the slab of a 1970s Westland ranch that has started leaking is a rerun, not a repair, and that labor is the same whether you keep the old equipment or not.
Question three: the 5,000 rule and the one-third rule
Two rules of thumb circulate in the trade and both are useful if you treat them as guides rather than laws.
The 5,000 rule: multiply the system's age in years by the repair quote in dollars. Under 5,000, repair; over 5,000, lean toward replacement. A 6-year-old system with a quote in the mid-hundreds is an easy repair. A 16-year-old system with a quote in the low thousands is not.
The one-third rule: if the repair costs more than roughly a third of what a new system would cost installed, replacement is the better value, because you are spending a third of the money to get zero of the new efficiency, warranty or refrigerant certainty.
For typical market pricing in Washtenaw and western Wayne County, a new 2- to 3-ton split system with a matched coil, installed by a licensed contractor with a permit, generally lands in the mid-four-figures to low-five-figures depending on efficiency tier, whether the furnace blower is being reused, and line-set and electrical work. That is market context, not a quote; our own AC installation estimates are free and specific to the house.
What a new system actually saves you
A 2005 condenser in a Canton subdivision was probably 10 or 12 SEER when new and is running below that now with a dirty coil and a tired compressor. The 2025 federal minimum for our region is 13.4 SEER2, and a reasonable mid-tier system is 15 to 17 SEER2. That is a 25 to 40 percent reduction in cooling electricity for the same comfort. In Southeast Michigan that is a modest number in dollars, because cooling season is short and DTE's summer rates are not Arizona's; most homeowners see the savings on the June through September bills but should not expect a new AC to pay for itself on efficiency alone. The stronger argument is reliability, humidity control and the refrigerant question.
A newer two-stage or variable-speed system also runs longer, lower cycles that pull more moisture out of the air, which on a 72-dew-point July afternoon in a humid Huron River valley basement is a real comfort change. Single-stage vs two-stage vs variable-speed covers whether that upgrade is worth it for your house.
Federal 25C tax credits exist for qualifying high-efficiency equipment, and DTE Energy runs rebate programs on qualifying central AC and heat pumps. Both change year to year, and both can tilt a borderline decision. We will tell you what applies at the time of your estimate.
Where we land in practice
The cases where we say "fix it." We have told a lot of homeowners not to replace. A 2012 R-410A system with a failed capacitor and a slow leak at a Schrader core gets a core, a vacuum and a charge, and it goes another five years. A 14-year-old unit with a bad contactor gets a contactor. A homeowner who was quoted a replacement by another company because the outdoor fan motor died gets a fan motor from us and a conversation about what to plan for. If the system is cooling the house, the repair is small, and the refrigerant is R-410A, there is no reason to spend five figures because of one failed part.
And the cases where we say "replace it." An R-22 system that needs any refrigerant beyond a pound. Any compressor failure on a system past 10 years. An evaporator coil leak on a 2008 install. A system that has needed a refrigerant top-off three summers in a row, which means the money has been going into leaked gas. A condenser that trips its breaker because the compressor windings are breaking down. And, honestly, a 20-year-old system that is working fine but that you are about to put a new furnace next to; matching the two saves a second install bill and a second disruption, and a matched system is the only way to get the rated efficiency.
How to use this before the next failure
The worst time to make this decision is at 4 p.m. on a 94-degree Friday with the house at 85. If your system is 12 or older, ask for an honest assessment during a spring AC tune-up: compressor amp draw against the data plate, capacitor microfarads, refrigerant pressures, coil condition. That gives you a year or two of warning and lets you shop replacement on your schedule, with rebates lined up and a Manual J done properly. How long do air conditioners last in Michigan has the full picture on what to expect by age.