This is the most common call we get in summer, and it usually comes from a homeowner who has already confirmed the system is doing something — the fan is running, the outdoor unit is humming — but the house keeps climbing.
1. A restricted air filter
It sounds too simple, but a clogged filter reduces airflow across the evaporator coil enough to drop capacity dramatically and, eventually, to freeze the coil. In a Tallahassee spring, a filter can go from clean to choked in a few weeks.
Pull the filter and hold it up to a light. If light does not pass through easily, replace it and give the system an hour.
2. A frozen evaporator coil
If the indoor coil is iced over, air cannot pass through it. You may see frost on the refrigerant line at the air handler. Turn the system to OFF and the fan to ON to thaw it, which can take several hours.
Ice is a symptom, not the disease. The cause is almost always restricted airflow or low refrigerant, and it will return if the cause is not addressed.
3. Low refrigerant from a leak
Refrigerant is not consumed. If the charge is low, there is a leak. Symptoms include weak cooling, longer run times, ice on the line set, and a home that struggles most during the hottest part of the afternoon.
Adding refrigerant without finding the leak is a temporary fix that will be repeated at your expense.
4. A dirty outdoor condenser coil
The outdoor coil rejects heat. When it is packed with pollen, grass clippings, and pine straw, the system cannot dump heat efficiently and capacity drops sharply on the hottest days — exactly when you need it.
5. A failing capacitor or contactor
If the outdoor fan spins but the compressor is not running, you often get room-temperature air out of the vents. A weak capacitor is a common, inexpensive failure — but it needs to be tested, not guessed at, and capacitors hold a dangerous charge.
6. Duct leakage in a hot attic
A system can be working perfectly and still lose a large share of its cooling into the attic through leaking ducts. This tends to show up as a house that cools acceptably at night and loses ground every afternoon as the attic heats up.
What to do next
Change the filter, confirm the thermostat is on COOL with the fan on AUTO, clear debris from the outdoor unit, and check for ice. If none of that resolves it within a few hours, the remaining causes involve refrigerant or electrical components and need a technician.
Frequently asked questions
- Should I keep the system running while I wait for service?
- If the coil is frozen or the breaker is tripping, shut it off. Otherwise, running it is generally fine, though a system that cannot keep up will simply run continuously.
- Can I add refrigerant myself?
- No. Refrigerant handling requires certification and equipment, and overcharging causes its own damage. Low charge also means there is a leak to find.