Short answer
Replace when the system is past about 12–15 years, uses R-22 and has a leak, or a repair costs more than about a third of a new system. Repair when it's under 10 years old and the failure is a single part like a capacitor, contactor or fan motor.
The age rule depends on climate
Long run hours shorten equipment life. A 15-year-old system in Phoenix, Las Vegas or Houston has worked as many hours as a much older one in a mild northern climate.
Refrigerant
R-22 is no longer produced. A large R-22 leak almost always tips the decision to replacement.
Efficiency and comfort
If some rooms never cool or bills keep climbing, a correctly sized new system with duct repairs may solve problems a repair can't.
- Ask for a Manual J load calculation
- Ask whether ducts will be tested
- Compare SEER2 ratings and warranties
Get it in writing
Ask for two options with model numbers, warranty terms and permit included, and verify the contractor's license with your state or local licensing authority.
A simple cost rule of thumb
Some homeowners use the "5,000 rule": multiply the system's age by the repair cost. If the result is above about 5,000, replacement deserves a serious look. It's a rough screen, not a verdict, and it ignores efficiency and comfort.
When repair clearly makes sense
Many failures are single, inexpensive parts on otherwise healthy equipment.
- Capacitor, contactor or fuse
- Clogged condensate drain or float switch
- Thermostat or wiring fault
- Blower or condenser fan motor on a system under about 10 years old
Plan replacement before it's an emergency
Replacing during peak heat often means longer waits and fewer equipment choices. If the system is old and needed several repairs last season, getting two quotes in spring or fall gives you time to compare sizing, efficiency and warranty terms.
Match the system, don't just swap boxes
A new outdoor unit should be matched with a compatible indoor coil or air handler. Mismatched equipment can underperform its rating and may affect warranty coverage.
Questions
How long do AC systems last?+
Often 12–17 years, and 10–15 years in very hot or coastal climates, depending on maintenance, sizing and installation quality.
Is it worth fixing a 15-year-old AC?+
For a minor part on a working system, yes. For a compressor failure, a large refrigerant leak or repeated breakdowns, replacement usually makes more sense at that age.
Can I replace only the outdoor unit?+
Sometimes, but matching the indoor coil and outdoor unit is generally recommended for rated efficiency and warranty. Ask the contractor whether the existing coil is compatible.
Editorial note: this guide is general information for homeowners, not a diagnosis. Desertline Heating & Air is a referral service; a licensed contractor should inspect your equipment before repairs.