Repair the AC if it's under 10 years old and the fix is a single component like a capacitor, fan motor, or contactor. Lean toward replacement if the system is 12 to 15 years old in Phoenix (which is the end of typical life here), if it uses R-22 refrigerant, if the repair is a compressor or evaporator coil, or if the repair quote is more than a third of a replacement quote. When it's close, get both quotes in writing and decide in the morning, not on a 112°F afternoon with a tech in the driveway.
The numbers that decide it
Age. Phoenix systems run nearly year-round, so 12 to 15 years is a full life here where the same unit might reach 18 elsewhere. A major repair on a 13-year-old Valley system buys less time than the same repair anywhere else.
Repair cost vs. replacement cost. A common rule: multiply the repair quote by the system's age in years. If the result exceeds roughly the replacement price, replace. A $1,500 repair on a 12-year-old system (18,000) against a $10,000 replacement points to replacement; a $400 repair on the same unit (4,800) points to repair.
Refrigerant. R-22 systems (generally pre-2010) are expensive to recharge and parts are scarce. Any refrigerant-related repair on an R-22 system is a replacement conversation.
Repeat failures. A second major repair within two summers usually means the system is at end of life, whatever the individual quotes say.
Repairs that almost always make sense
Capacitors, contactors, fuses, thermostats, drain line clogs, float switches, and fan motors on systems under about 12 years. These are inexpensive relative to replacement and don't signal that the rest of the system is failing.
A single refrigerant leak at a fitting or valve on an R-410A system under 10 years old. Repair and recharge, then watch it.
Blower motors and control boards on newer systems, especially under parts warranty where you pay labor only. Check the data plate for the install date before assuming there's no coverage.
Replacements that almost always make sense, and how to not get oversold
Compressor failure on a system over 10 years, an evaporator coil leak on an R-22 system, or a repair quote that approaches half the replacement price. Also: a system that can't hold the house below 80°F on the hottest days even when working, which is a capacity or duct problem a repair won't fix.
To avoid being oversold: ask for the diagnosis in writing with readings, ask what the repair would cost even if the tech recommends replacement, and get a second replacement quote before signing. A legitimate replacement recommendation survives a night's sleep and a second opinion.
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