An AC that runs constantly but can't pull the house below 78 or 80°F on a 100-plus-degree Sacramento afternoon has one of a few root causes, and the fix depends on which.
Dirty coils are the most common. A dust-caked evaporator coil and a cottonwood-fluff-packed condenser both reduce heat transfer. The system runs longer and longer cycles trying to move heat that isn't being moved efficiently. Coil cleaning — condenser first because it's easier to reach — restores capacity on most systems.
Low refrigerant is the second most common cause. A system low on refrigerant can't absorb enough heat at the evaporator. You'll often see ice forming on the suction line near the air handler. Refrigerant is a closed loop, so low charge means a leak — find the leak, fix the leak, evacuate, and recharge to the manufacturer's spec.
Undersized equipment is a structural problem, not a repair. If the system has always struggled during heat waves, it may genuinely be too small for the home — common in older Sacramento homes that had additions built without upsizing the HVAC. Manual J load calculations confirm the diagnosis; the fix is replacement with correctly sized equipment.
Duct leakage in the attic is the hidden one. Sacramento attics hit 140°F-plus in summer. A duct system with 20 percent leakage is dumping conditioned air into the hottest part of the house and pulling hot return air in through the ductwork. A duct blaster test quantifies the leakage; sealing and re-insulating the ducts can add 2 to 4°F of cooling capacity at the registers.