By Home HVAC, Plumbing & Electrical · July 2, 2026 · 6 min read
The short answer
If your air conditioner runs but doesn't cool, the usual causes are a dirty air filter, wrong thermostat setting, a frozen evaporator coil, a tripped breaker, a dirty outdoor condenser, or low refrigerant. Start with the filter and thermostat—those two explain most no-cool calls—then check for ice or a tripped breaker before calling a pro.
The 7 most common reasons an AC won't cool
| # | Cause | How you'd notice | DIY-fixable? |
|---|---|---|---|
| 1 | Dirty air filter | Weak airflow from vents | Yes—replace it |
| 2 | Wrong thermostat setting | Set to "fan/on," not "cool/auto" | Yes |
| 3 | Frozen evaporator coil | Ice on the indoor unit, no cold air | Thaw, then diagnose |
| 4 | Tripped breaker / outdoor unit off | Indoor fan runs, outdoor unit silent | Reset once |
| 5 | Dirty condenser coil | Outdoor unit caked in dirt/debris | Partly |
| 6 | Low refrigerant / leak | Poor cooling, hissing, higher bills | No—pro only |
| 7 | Failing compressor/capacitor | Outdoor unit hums, won't start | No—pro only |
What should I check first?
- Thermostat: set to Cool, fan to Auto, at least 5°F below room temp.
- Filter: if it's gray/clogged, replace it—a dirty filter chokes airflow and can freeze the coil.
- Breaker: reset a tripped AC breaker once; if it trips again, stop and call a pro.
- Outdoor unit: confirm the fan spins and the coil isn't buried in grass or leaves.
Why is ice forming on my AC?
A frozen coil almost always traces to restricted airflow (dirty filter, blocked returns) or low refrigerant. Switch to "fan only" to thaw fully, replace the filter, and if it re-freezes, that points to refrigerant—an EPA-certified-tech repair, not DIY. Not sure how old your filter is? See how often to change your HVAC air filter.
When should I call a professional?
Call a pro if the breaker trips repeatedly, you suspect a refrigerant leak, the coil keeps freezing after a filter change, or the outdoor unit hums but won't start—those involve refrigerant, electrical, or compressor work.
Not cooling and can't pin it down? Schedule AC repair with our Sedalia team or call (660) 827-0101. Serving Sedalia and Mid-Missouri, 24/7.
Need a pro to take it from here?
Serving Sedalia and Mid-Missouri since 1960 — with 24/7 emergency service when it can't wait.
Frequently asked questions
Why is my AC running but the house is still hot?
Usually a dirty filter, a thermostat set to "fan" instead of "cool," a frozen coil, or low refrigerant. Check the filter and thermostat first.
Can a dirty filter stop my AC from cooling?
Yes—a clogged filter restricts airflow and can freeze the evaporator coil, cutting off cold air.
Is it safe to run my AC when it isn't cooling?
If the coil is frozen or the breaker keeps tripping, turn it off—running it can damage the compressor.