What should I do if my AC runs constantly or will not shut off?

What continuous AC operation usually means

An air conditioner is supposed to run longer on very hot afternoons, but it should still cycle off after it removes enough heat to satisfy the thermostat. When it runs continuously, the key question is whether it is cooling too slowly or whether part of the system is being told to run when it should be off. That distinction matters because a nonstop blower points toward fan-control or thermostat issues, while a nonstop outdoor unit points more toward a stuck contactor or a cooling system that cannot keep up.

What you can tell from what keeps running

Listen for whether the indoor airflow continues by itself, the outdoor unit continues by itself, or both stay on together. If the fan keeps blowing from the vents after the temperature setting is reached but the outdoor unit is off, the thermostat may be set to FAN ON instead of AUTO, or the fan relay/control may be sticking. If the outdoor condenser keeps humming and the top fan keeps spinning even after the thermostat is satisfied, that is more consistent with a contactor that is stuck closed and needs service.

Signs the system is running nonstop because cooling capacity has dropped

If the AC runs all day and the indoor temperature falls only a degree or two every hour, the system is probably not moving enough heat. Common clues are air that feels only mildly cool instead of distinctly cold, ice on the larger copper line, water around the air handler after thawing, or an outdoor unit that feels extremely hot and seems to struggle in the afternoon. Those symptoms fit low refrigerant, evaporator icing, or a condenser that cannot reject heat, not a simple on-off control problem.

What a technician usually checks on this call

A service visit for this symptom typically starts with cycle behavior: whether the thermostat is calling correctly, whether the blower and outdoor unit respond normally, and whether either one keeps running after the call ends. The technician will then check temperature split across the indoor coil, amperage draw of the compressor and fan motors, condenser coil condition, refrigerant pressures, and whether the contactor is opening and closing properly. If icing is present, they may need the system thawed before final measurements are accurate.

What affects repair cost

Cost depends heavily on whether the problem is a control issue or a cooling-capacity issue. Thermostat replacement or rewiring is often in the roughly $188-$607 range, and a contactor replacement commonly falls around $188-$607. Condenser fan motor repairs often run about $373-$1,467, while refrigerant leak diagnosis and sealed-system repairs can range from several hundred dollars into $1,500 or more before any refrigerant is added, depending on leak location, refrigerant type, and accessibility.

If the system is running constantly during a severe heat wave, some extended run time can be normal, especially in direct sun or poorly insulated homes. But if it runs through cooler evening hours without catching up, if the outdoor unit will not shut off, or if you see ice, water, or overheating, that is no longer just weather-related demand. Those observations help narrow the problem quickly and are useful details to share when you book service.