The industry 5,000 rule: multiply the repair quote by the equipment age in years. Above $5,000, replacement usually wins; below, repair. Bound it by expected life (15 to 20 years for AC and heat pumps, 20+ for furnaces) and by refrigerant: R22 systems are obsolete, R410A is being phased down for low-GWP A2L refrigerants like R454B.
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Replace or Repair: The HVAC Decision Guide
The 5,000 rule, lifespan, and refrigerant phaseouts.