Check the thermostat and filter first
Confirm COOL mode, a realistic temperature setting and a filter that is not badly restricted.
Airflow problems can mimic an AC failure
A dirty filter, frozen indoor coil, blower problem or blocked return can reduce the amount of cool air reaching the rooms.
The refrigeration system may need diagnosis
Low refrigerant from a leak, compressor problems, dirty coils or other refrigeration faults can allow the equipment to run without providing normal cooling.
Running longer is not the same as cooling properly
If the system runs continuously but indoor temperature does not fall, professional diagnosis is appropriate.
Check whether both the indoor blower and outdoor condenser are operating. That simple observation helps narrow the next diagnostic step.
Check whether the system is actually in a cooling cycle
Set the thermostat to COOL, lower the setpoint below room temperature and set the fan to AUTO for basic troubleshooting. If only the indoor fan is running, room-temperature air can feel like the AC is operating when the outdoor cooling equipment is not.
Weak airflow can make normal cooling impossible
A dirty filter, blower problem, blocked return or frozen indoor coil can reduce the amount of air moving across the evaporator. If airflow is much weaker than normal, the issue may be inside rather than at the outdoor condenser.
Outdoor-unit operation is another useful clue
If the thermostat is calling for cooling but the outdoor unit does not run, electrical controls, a contactor, capacitor, wiring or other components may be involved. Do not open energized electrical compartments.
If the system runs continuously and the house stays warm
Dirty coils, refrigerant-system problems, compressor performance, airflow, duct losses or an unusually high building load may all contribute. Professional measurements are needed to separate these causes.
Frequently asked questions
Why is the outside AC running but the house is warm?
Possible causes include weak indoor airflow, dirty coils, refrigerant-system problems, compressor performance, duct issues or a cooling load the system is not meeting.
Should I turn the AC off if the coil is frozen?
Yes. Turn cooling off and allow the ice to thaw. Do not chip the ice away. Recurring freezing needs diagnosis.
Can a dirty filter cause poor cooling?
Yes. A severely restricted filter can reduce airflow across the indoor coil and reduce system performance.
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