AC Not Cooling? Here's How to Troubleshoot It

Your AC is running, but the house isn't cooling down. In Miami, that's not just inconvenient — it can be dangerous. Before you call a technician, work through this checklist. Some of the most common causes are things you can fix yourself in minutes.

Step 1: Check Your Thermostat Settings

It sounds obvious, but confirm:

• The thermostat is set to COOL, not HEAT or FAN ONLY
• The setpoint is lower than the current room temperature
• The fan is set to AUTO, not ON (ON runs the fan continuously without cooling)
• Batteries are fresh if it's a battery-operated thermostat

Step 2: Check Your Air Filter

A severely clogged filter restricts airflow so badly that the system literally cannot move enough air to cool your home — and it can cause the evaporator coil to freeze. Pull out the filter and hold it up to the light. If you can't see light through it, it needs to be replaced immediately. This is the #1 cause of poor AC performance and it costs $5–$15 to fix.

Step 3: Check Your Circuit Breaker

Look at your electrical panel for the AC breaker — it's usually a double-pole breaker labeled "AC," "Air Handler," or "Condenser." If it's tripped (in the middle position), switch it fully off, wait 30 seconds, then switch it back on. A repeatedly tripping breaker indicates an electrical problem that requires a technician.

Step 4: Inspect the Outdoor Unit

Go outside and look at your condenser unit (the big box outside). Check for:

• Is it running? — You should hear the compressor and fan motor. If it's silent, the problem is likely electrical (capacitor, contactor, or power issue).
• Is the fan spinning? — A running compressor with a stopped fan motor is a common failure point.
• Is it blocked? — Clear any debris, leaves, or vegetation within 2 feet of the unit.
• Is there ice forming? — Ice on the refrigerant lines or coil means the system is frozen up (see our article on this).

Step 5: Check Your Vents and Registers

Walk through your home and make sure all supply and return vents are open and unobstructed by furniture, curtains, or rugs. A blocked return vent starves the system of air to cool and is a surprisingly common culprit.

Step 6: Check the Condensate Drain Pan

Look under your indoor air handler. If you see water overflowing from the drain pan, the condensate drain line is clogged. Many modern systems have a float switch that shuts down the entire system when this happens — as a safety feature to prevent water damage. Clearing the drain line (flush with a wet-vac or diluted vinegar) will restore operation.

When to Call a Professional

Call us if you've gone through the checklist above and still have problems, or if you notice:

• Ice on any part of the system
• Unusual noises (grinding, squealing, banging, hissing)
• A burning or musty smell from the vents
• The breaker keeps tripping after reset
• The system runs constantly but never reaches setpoint
• You suspect a refrigerant leak (hissing sound, oily residue near lines)