The short answer
When the air is warm but the fan is running, the outdoor unit is usually not doing its share. The usual causes are a failed capacitor or contactor, a condenser fan motor that has stopped, or a refrigerant charge that has gone low. It is usually a repair.
What you can check yourself
- Set the thermostat to Cool, and below the room temperature.
- Check that the filter is not packed with dust.
- Look at the outdoor unit: is the fan turning? Clear leaves and grass away from it.
- Check that the breaker has not tripped. Reset it once at most.
What gets checked first
- Capacitor and contactor at the condenser
- Condenser fan motor
- Refrigerant charge and the coil
- The filter, if it has been a while
Repair or replace?
Usually a repair. A failed capacitor is the most common part on the truck.
When to call now
Do not take the panel off the outdoor unit yourself. A capacitor can hold a charge after the power is off.