AC Not Cooling? What to Check First
Quick Answer: If your AC is running but not cooling, first check that the thermostat is set to COOL and below room temperature, replace a dirty air filter, reset a tripped breaker once, and look for a clogged condensate drain or ice on the refrigerant lines. If it still isn't cooling after these checks, turn the system off and call a licensed technician.
Safety first
Turn the system off at the thermostat before touching the filter or drain line. Don't open electrical panels on the unit, handle refrigerant, or keep resetting a breaker that trips again. Call a pro. Call right away for burning smells, smoke, buzzing at the outdoor unit, or water coming through a ceiling.
1. Check the thermostat
- Set to COOL (not FAN or HEAT) and a few degrees below the room temperature.
- Fan on AUTO, not ON. With ON, the fan keeps blowing even when the system isn't cooling.
- Replace batteries if the display is blank or dim.
- FPL recommends 78°F (or the highest comfortable setting) when you're home in summer. A system that "won't go below 75" on a 95°F afternoon may be working normally.
2. Replace the air filter
A clogged filter restricts airflow, can freeze the indoor coil, and makes the system run longer. ENERGY STAR recommends checking the filter monthly and warns a dirty filter can raise energy costs and damage equipment.
3. Check the breaker and outdoor unit
- If the outdoor unit is silent while the indoor fan runs, check for a tripped AC breaker. Reset it once. If it trips again, stop and call. Repeated trips point to an electrical or compressor problem.
- Keep the outdoor unit clear of plants, debris and shutters.
4. Look at the condensate drain (very common in South Florida)
High humidity means your AC pulls a lot of water from the air. If the drain line clogs, a float switch can shut the system off or the pan can overflow. Look for standing water in the pan or around the air handler. ENERGY STAR recommends inspecting the condensate drain.
5. Look for ice
Ice on the copper lines or indoor coil usually means low airflow (dirty filter, closed vents) or low refrigerant. Set the system to OFF and the fan to ON for a few hours to thaw, replace the filter, then try again. If it freezes again, call. Low refrigerant means a leak that a licensed technician must find and repair.
6. Open vents and check for duct problems
Make sure supply vents and returns aren't closed or blocked. Weak airflow in one or two rooms can mean a disconnected duct.
When to call a pro (24/7: 645-232-5522)
- Still not cooling after these checks
- Breaker trips again after one reset
- Ice keeps coming back
- Outdoor unit hums or clicks but its fan doesn't spin
- Burning smell, smoke, or water in ceilings or walls
- Vulnerable people at home during high heat
FAQ
Why is my AC running but not cooling the house?
The most common causes are a dirty air filter, a thermostat set to FAN or the wrong mode, a tripped breaker that shut off the outdoor unit, a clogged condensate drain, or a frozen coil. Low refrigerant and failed capacitors also cause it, and those need a licensed technician.
Why is my AC not cooling but the fan is running?
If the indoor fan runs but the air is warm, the outdoor unit often isn't running. Check the breaker and thermostat mode. If the outdoor unit hums but its fan doesn't spin, a capacitor or contactor may have failed. Call a technician.
Why is my AC not cooling below 75?
On very hot, humid South Florida days, a correctly sized system may struggle to get much below the mid-70s. FPL recommends 78°F in summer. If it can't reach a normal setting on milder days, check the filter and coils or schedule a diagnostic.
How do I reset my AC unit?
Turn the thermostat off, switch off the AC breaker (and the outdoor disconnect if you have one) for about 5 minutes, switch them back on, then set the thermostat to COOL. If the breaker trips again, don't keep resetting it. Call a pro.
What should I do if my AC drain line is clogged?
Turn the system off, check the drain pan for standing water, and clear the line at its cleanout or outdoor outlet if you can do it safely. If water has reached the ceiling or the system won't restart, call for service.
Still not cooling? We answer 645-232-5522 24/7 across Miami-Dade and Broward.
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