AC running constantly? When it's normal and when it isn't

First: is it actually a problem?

Long run times aren't automatically bad. A correctly sized system is designed to run for long cycles on the hottest days, and variable-speed systems are meant to run almost continuously at low speed. That's how they remove humidity.

It's worth investigating when:

• The house never reaches the set temperature, even in the evening.
• It runs non-stop on mild days or at night, when it used to cycle off.
• The air from the vents is only slightly cooler than the room.
• Your electric bill jumped compared with the same month last year.

Checks you can do

1. Thermostat: set to Cool, fan on Auto (with On, the blower runs all the time, which isn't the same as cooling). A very low set point, like 68°F, can keep a system running all afternoon.
2. Filter: replace it if it's dirty. Restricted airflow makes the system run longer for less cooling.
3. Outdoor unit: clear debris and anything within two feet. A coil packed with grass or salt can't shed heat.
4. Ice: check the copper line and the indoor coil. If there's ice, turn cooling off (see frozen AC coil).
5. Windows and doors: sun-facing glass, an open garage door into the house, or a leaky attic hatch can overwhelm a system on a hot day.

Causes a technician looks for

• Low refrigerant from a leak: the system runs longer and cools less.
• Dirty indoor or outdoor coil: heat transfer drops.
• Leaky ducts in a hot attic: cooled air never reaches the rooms. ENERGY STAR estimates typical duct systems lose around 20–30% of their air.
• A contactor stuck closed: the outdoor unit keeps running even after the thermostat is satisfied. Turn the system off at the breaker and call.
• An undersized or aging system that can no longer keep up with the home's real load. A Manual J load calculation answers whether the size was ever right.

When to call

Call if the house won't reach the set temperature by evening, if the outdoor unit keeps running with the thermostat off, or if you see ice. We diagnose first and give you a flat written price before any repair. If the system is undersized or near the end of its life, we'll explain the repair-versus-replace options honestly.