The AC is running, the thermostat is set to 72, and the house is still 80. Frustrating — but usually fixable. Here are the 12 most common causes, in order from "easy DIY" to "call a pro."
Try These First (DIY, Free)
1. Thermostat set wrong
Sounds dumb, but happens constantly. Make sure it's set to COOL (not heat or fan), the temp is below the current room temp, and the fan is on AUTO (not ON).
2. Clogged air filter
If your filter looks gray and dusty, replace it. A clogged filter can drop cooling capacity 30%.
3. Closed or blocked supply vents
Walk through the house. Make sure no vents are closed or blocked by furniture. Closing too many vents builds up duct pressure and reduces overall cooling.
4. Blocked outdoor condenser
Walk outside to your AC unit. Make sure there's no grass, leaves, mulch, or debris covering the coil. Should have at least 2 feet of clearance on all sides. Spray with garden hose (top-down only, never up).
5. Tripped breaker
Check the electrical panel for a tripped AC breaker. Reset once. If it trips again, stop — that's an electrical issue, call a pro.
Probably Need a Tech (Cheap Fixes)
6. Failed capacitor ($165–$295 to fix)
The #1 cause of "AC running but not cooling" calls. The capacitor is what kicks the compressor and fan motor on. When it fails, the system runs but doesn't actually cool. 20-minute fix.
7. Burned contactor ($180–$325)
The electrical switch that turns the compressor on. When contacts burn out, the system runs intermittently or not at all.
8. Clogged condensate drain line ($129–$225)
Most modern systems shut off the compressor when the drain line backs up (safety switch). If you've seen water around the air handler OR the system suddenly stopped working, this is likely.
9. Low refrigerant ($245–$495)
Look for: warm air at vents, ice on the copper refrigerant line, hissing sound near the line set. Low refrigerant means there's a leak somewhere — we find it, fix it, then recharge.
More Serious (Bigger Repairs)
10. Frozen evaporator coil ($245–$595)
If the indoor coil is iced over, the system can't transfer heat. Causes: low refrigerant, dirty filter, blower problem. Don't run it — turn the system off, let it thaw 4 hours, then call us.
11. Failed blower motor ($425–$895)
The indoor fan that moves air through your ducts. If it fails, you get little to no airflow at vents — even though the outdoor unit may seem to be running.
12. Failed compressor ($1,800–$3,500)
The worst-case scenario. The compressor is the "heart" of the AC — when it dies, you usually replace the whole outdoor unit. If your system is 10+ years old, replacing the entire AC often makes more sense.
What to Do Right Now
- Try the 5 DIY fixes (5 minutes total)
- If no luck, turn the system OFF and call us
- Don't keep running it — you can turn a $200 fix into a $2,000 problem in hours
Need same-day AC repair? Call (855) 417-8866. Average response: 47 minutes across South Florida.