A system has failed and there is a repair quote. Whether to spend it comes down to four questions.
1. How old is it
Typical service life for residential cooling equipment is 12 to 18 years, shorter in coastal environments and in systems that have short cycled for years.
The often-quoted $5,000 rule multiplies the age in years by the repair cost; over $5,000 suggests replacement. It is a rough heuristic and it captures the right idea — that money spent on old equipment buys fewer remaining years.
2. What refrigerant does it use
This is frequently the deciding factor.
R-22 was phased out of production and import. Servicing an R-22 system now means reclaimed or stockpiled refrigerant at a price that can exceed the value of the repair. A system needing a significant R-22 charge is generally not worth repairing.
R-410A is now itself being phased down under the AIM Act, with new residential equipment moving to R-454B and R-32. R-410A will remain serviceable for years, but its cost trend is upward and it is worth factoring into a decision on equipment that is already old.
3. What has failed
Capacitor, contactor, fan motor — inexpensive, routine, worth doing on almost any system that is otherwise working.
Condenser fan or blower motor — moderate, usually worth it below about twelve years.
Evaporator coil leak — expensive, and on an older system often the point at which replacement wins, particularly if the coil is a discontinued part.
Compressor — the most expensive single component. On anything over roughly ten years old, a compressor quote is usually a replacement decision in disguise.
4. How is it running otherwise
A system that has been keeping up, cycling reasonably and holding humidity is worth repairing further into its life than one that has never been comfortable.
If the house has been humid and the rooms uneven for years, the equipment was probably always the wrong size, and a repair buys more years of the same complaint.
The arguments for replacing sooner
A failure in July is an emergency, and emergency replacements are chosen under pressure with whatever is on the truck. A planned replacement in the shoulder season gets better equipment, better pricing and a Manual J.
Efficiency gains are real against genuinely old equipment. A 10 SEER system from the 1990s replaced with modern equipment is a large step, though the same comparison against a 14 SEER unit from 2012 is much less compelling.
Incentives — federal credits and utility rebates change the arithmetic, and they apply to replacement rather than repair.
The arguments for repairing
The existing system is under fifteen, uses R-410A, the failure is a component rather than the compressor or coil, and the house has been comfortable.
In that case a repair is usually the better value, and the replacement can be planned rather than forced.
What to do either way
Get the load calculation done now, while there is time. If the decision is repair, the number is ready for whenever the system does fail.
And look at the ducts. On a replacement, correcting duct leakage and adding attic insulation before sizing frequently allows a smaller system — which is the one place in this decision where spending money reduces the total bill.
The indoor coil question
On a replacement, the indoor coil must be matched to the new outdoor unit. A quote that replaces the condenser and leaves an older coil in place saves money now and gives up the rated efficiency, because the AHRI rating applies to the tested combination.
It also leaves a component of unknown remaining life inside the system, which is the part that is expensive to reach later.
Getting a second opinion on a large repair
For anything at compressor or coil scale, a second diagnosis is cheap relative to the number being quoted.
Ask specifically what was measured — superheat, subcooling, static pressure — rather than what was concluded. A diagnosis backed by readings is one you can take to a second contractor and compare; a diagnosis without them is not.