In order of how often they are found: a clogged filter or blocked airflow, a failed capacitor or fan component, low refrigerant from a leak (refrigerant is not consumed; low means leaking), a frozen coil from any of the above, and duct failures dumping cooled air into the attic. Runtimes of many hours without reaching the set point are the classic forum complaint and they sort into the same list. Turn a frozen system off and run the fan to thaw it, and never approve a refrigerant recharge without a leak search; topping off a leaking system is a subscription, not a repair.
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