Age alone is not a verdict
An older unit with a minor repair can differ from a newer unit with a major failed component.
Repeated failures change the economics
Several unrelated repairs in a short period can indicate declining reliability.
System fit matters
Replacement equipment should be selected and installed for the building rather than chosen only by brand or headline efficiency.
Get the scope, not just the box price
Duct, electrical, controls, drainage, ventilation and commissioning can influence the result.
Safety boundary. General planning information only. Do not open, dismantle or work on hazardous electrical, gas, structural, fire-protection or contaminated-water systems unless you are appropriately qualified and authorized.