Your Thermostat
It sounds obvious, but thermostats are the #1 false alarm in AC troubleshooting. Verify that the thermostat is set to “Cool” (not “Heat,” “Off,” or “Fan Only”), the set temperature is at least 3–5 degrees below the current room temperature displayed, and the batteries are not dead — a blank screen usually means dead batteries, not a dead AC system. If you have a smart thermostat, check whether a schedule or geofencing setting has changed the target temperature without your knowledge.
Fixes: Thermostat set incorrectly, dead batteries, schedule override.
Cost: Free.
Your Circuit Breaker
Locate your electrical panel and check the HVAC breaker (it may be labeled “AC,” “HVAC,” “Compressor,” or “Air Handler” — some systems have two breakers). If the breaker is tripped (in the middle position, not fully “On”), reset it by flipping it fully to “Off” and then back to “On.” Wait 3–5 minutes for the system to restart. If the breaker trips again immediately, do NOT reset it a second time — this indicates an electrical fault that requires professional diagnosis. Repeated resetting can cause further damage.
Fixes: Power interruption from storm, momentary overload.
Cost: Free.
When to stop: Breaker trips again immediately = call a technician.
Your Air Filter
A clogged air filter is the single most common preventable cause of AC performance problems. A severely restricted filter reduces airflow to the point where the evaporator coil freezes over, the system runs continuously without reaching temperature, or the blower motor overheats and shuts down. Remove your filter and hold it up to a light source: if you cannot see light through it, it needs replacement. In Jacksonville’s environment, standard 1-inch filters should be replaced every 30–60 days during summer and every 60–90 days during mild seasons.
Fixes: Reduced airflow, frozen coil (secondary), blower motor strain.
Cost: $5–$25 for a replacement filter.
Your Vents
Walk through your home and verify that all supply vents (the ones that blow air) and return vents (the ones that pull air) are fully open and not blocked by furniture, curtains, rugs, or stored items. A single blocked return vent can reduce system airflow significantly. Also check that the vent louvers are angled open, not closed — a well-intentioned family member or cleaning service may have closed vents in unused rooms, creating pressure imbalances that affect the entire system.
Fixes: Airflow restriction from blocked or closed vents.
Cost: Free.
Your Outdoor Unit
Go outside and look at the outdoor condenser unit. Is it running? Can you hear the fan and compressor? If it is silent while the indoor system is running, the outdoor unit may have lost power (check its dedicated breaker), the contactor may have failed, or the capacitor may have died — the latter two require professional repair. If the unit is running, check for debris: leaves, grass clippings, dirt, and vegetation within 2 feet of the unit restrict airflow and reduce efficiency. Clear any obstructions and rinse the coils gently with a garden hose (power the system off first).
Fixes: Debris restriction, separate breaker tripped.
Cost: Free (debris clearing) or professional repair (contactor/capacitor).
Your Condensate Drain
The condensate drain carries moisture removed from your home’s air to the outside. In Jacksonville’s humidity, this drain handles a significant volume of water daily. If it clogs with algae, mold, or debris, many modern systems have a safety float switch that shuts the system down to prevent water damage. Find where the PVC drain line exits your home (usually near the outdoor unit or along the foundation) and verify water is dripping during operation. If the system is off and the drain appears clogged, you can try flushing it with a cup of white vinegar or dilute bleach poured into the access point on the indoor drain pan. If you cannot locate the drain or are unsure, this is a quick professional fix.
Fixes: Safety shutoff from clogged drain (very common in Jacksonville).
Cost: Free (DIY flush) or $100–$200 professional clearing.
Condensate drain clogs are disproportionately common in Jacksonville’s humidity. This check alone resolves a meaningful percentage of summer “AC not cooling” calls.
Ice on the System
Look at the indoor evaporator coil (visible through the air handler access panel) and the outdoor refrigerant lines (the copper lines running between indoor and outdoor units). If you see ice forming on either, your system is freezing up. Common causes: dirty filter (restricting airflow — see Check 3), low refrigerant from a leak, or a failing blower motor. If ice is present, turn the system OFF at the thermostat and set the fan to “On” (not “Auto”) to circulate warm air over the frozen coil and melt the ice. This takes 2–4 hours. Do NOT continue running the system in cooling mode with ice present — it forces the compressor to work against restricted airflow and can cause permanent compressor damage.
Fixes: Frozen coil from filter, low refrigerant, or blower issue.
Cost: Free (if filter was the cause) or professional repair (refrigerant leak, blower motor).
Wait time: 2–4 hours for ice to melt before restarting.