You walk into your living room and immediately notice it's warm. The thermostat reads 78°F but you set it to 72°F. The outdoor unit is humming, the fan is spinning, you can hear air moving through the vents — but nothing is actually getting cool. This is one of the most common service calls I take in Tampa Bay. Here are the 8 most likely causes, ordered from cheapest to fix to most expensive, with what you can safely check yourself before calling.
Quick safety check before troubleshooting: if you smell anything burning, see ice forming on the refrigerant lines, or hear loud grinding/screeching, turn the system off at the thermostat now and call for service. Continuing to run a system in these states can turn a $300 repair into a $2,000 one.
1. Dirty Air Filter (Cost: $15)
Always check this first.A clogged filter restricts airflow over the evaporator coil, which causes two problems: the air your system can deliver gets reduced (so cooling feels weak), and the coil temperature drops too low and starts to freeze. A frozen coil can't transfer heat at all — at that point, your system blows warm air no matter how cold the refrigerant is.
What to do:Pull the filter out and look at it. If you can't see light through it, replace it. In Tampa during summer, replace filters monthly. If the filter looks fine, move to step 2.
2. Thermostat Issue (Cost: $0–$200)
Sometimes the thermostat is the problem, not the AC. Check three things: (a) is it actually set to cool mode and not fan or heat? (b) is the temperature setting at least 3°F below current room temp? (c) does the thermostat screen show a low-battery indicator?
What to do:Replace thermostat batteries if applicable. Reset to a clearly lower setting (e.g. 68°F) and wait 5 minutes. If the system still runs but doesn't cool, the thermostat may be miscalibrated or failing. A new programmable or smart thermostat installed runs $200–$400.
3. Frozen Evaporator Coil (Cost: $0–$200 if caught early)
If you go look at the indoor air handler (usually in your attic, garage, or a closet) and see ice on the copper refrigerant linesor on the coil itself, that's a frozen evaporator. This is almost always caused by either a dirty filter (see #1), low refrigerant (see #6), or a problem with the blower motor.
What to do: Turn the system to fan onlyfor 2–3 hours. This lets the ice thaw without the compressor running (which would damage it). Once thawed, run the AC again. If it freezes back up within a day, you almost certainly have low refrigerant or a blower motor problem and you need a tech.
4. Dirty Outdoor Condenser Coil (Cost: $150–$300)
The outdoor unit (the loud box in your yard) is responsible for dumping the heat your AC pulls out of your home into the outside air. If the fins on the outdoor coil are caked with grass clippings, pollen, dust, leaves, or pet hair, the system can't shed heat effectively — so the indoor air gets less cool, even though the system is “running.”
What to do:With the system off at the breaker, you can rinse the outdoor coil with a garden hose (gentle pressure, top to bottom). Don't use a power washer — it bends fins. If the coil looks heavily impacted, schedule a professional coil cleaning; in Tampa, this should be part of a twice-yearly tune-up anyway.
5. Failed Capacitor (Cost: $150–$350)
The capacitor is essentially a battery that helps start the compressor and fan motors. When it fails, the system might run partially — sometimes the outdoor fan spins but the compressor doesn't kick on, sometimes everything runs but at reduced power. Capacitors are the most common failure point on Florida AC systems because Tampa heat literally cooks them.
What to do:This requires a tech. A capacitor swap is a 30-minute job and runs $150–$350 typically. The good news: this is a cheap, common repair, and once replaced your system should work like new. If your tech finds the capacitor failed, ask whether it's worth installing a higher-rated capacitor — they're only $20–$40 more and tend to last 2x as long in Florida heat.
6. Low Refrigerant / Refrigerant Leak (Cost: $300–$1,500)
AC systems are sealed — they shouldn't lose refrigerant under normal operation. If yours is low, you have a leak somewhere. Symptoms include: ice on the refrigerant lines, hissing sounds near the indoor or outdoor unit, weak cooling that gets worse over time, or a system that runs constantly without reaching the set temp.
What to do:Refrigerant work requires EPA certification, so this is a tech-only fix. The repair has two parts: find and fix the leak, then recharge the system. Small leaks are typically $300–$600 to fix; bigger leaks (like at the evaporator coil or compressor) can run $800–$1,500. If your system uses R-22 (phased out in 2020) and you have a leak, replacement is often cheaper than refilling.
7. Failing Compressor (Cost: $1,500–$3,500)
The compressor is the heart of your AC — it pressurizes refrigerant so heat can be transferred. When it starts to fail, you typically hear changes (louder operation, clicking, humming) and see reduced cooling capacity that gets worse over weeks or months. A fully failed compressor produces no cooling at all.
What to do:Compressor replacement on a 10+ year old system rarely makes financial sense. By the time you pay for the part ($800–$1,500) plus labor and refrigerant, you're at $1,500–$3,500 — and the rest of the system is the same age, meaning another major component is likely to fail soon. We always quote both the repair cost and a replacement option side-by-side so you can choose with full information.
8. Undersized System (Cost: Replacement)
Less common but worth mentioning: sometimes a system that's technically working can't actually cool the home because it's undersized. This happens when someone added a sunroom, finished a garage, or did anything that increased the cooling load without upgrading the system. The AC runs constantly trying to keep up but never reaches the set temperature on hot days.
What to do:A tech can verify this with a Manual J load calculation. If the system is genuinely undersized, options are: (a) replace with a properly-sized system, or (b) supplement with a ductless mini-split for the problem area. We commonly install mini-splits for sunrooms, additions, and garages where extending central AC isn't practical.
When to Call Right Away
Don't wait if you notice any of the following — these can cascade into much bigger problems within hours:
- Burning smells coming from the vents or the outdoor unit
- Loud grinding or screeching from the outdoor unit
- Water pooling around the indoor air handler or dripping from the ceiling
- Ice on the refrigerant lines that doesn't thaw within a few hours of the system off
- Tripping breakers when the AC tries to start
- The outdoor unit not running at all while the indoor blower runs
Need a Tampa Bay HVAC Tech Now?
We offer same-day AC repair across Tampa Bay with most service calls scheduled within hours of your call. Diagnostic fees are waived if you proceed with the repair, and every quote is in writing before any work starts. Call (813) 291-6146 or request service online.