AC running but not cooling — what to check
Check the safety items below first. Then: thermostat on Cool and below room temp, the filter clean, both the indoor and outdoor breakers on, and the outdoor unit's fan spinning. If the indoor coil or refrigerant line is iced up, turn the AC off and run just the fan to thaw it — a frozen coil blows warm air. If it's low on refrigerant or the compressor won't start, that's a licensed tech; topping up refrigerant isn't a DIY job.
First, a safety check — is any of this true right now?
No hazard flagged — the diagnostic steps below are appropriate. If any of the above changes, stop and follow the safety guidance.
Warm air has a few common causes
A dirty filter or a frozen evaporator coil restricts airflow so the air feels warm — turn the system to fan-only for a few hours to thaw ice, then replace the filter. After a power outage, some systems need a few minutes before the compressor restarts; wait 5–10 minutes before assuming a fault. If the outdoor fan runs but the compressor doesn't, or vice versa, that's a component fault.
What isn't DIY
Refrigerant (Freon) is a closed system — if it's low, there's a leak, and both handling refrigerant and finding the leak are licensed work. A compressor that hums but won't start, or repeated breaker trips on the AC circuit, also need a technician. A diagnostic visit is an estimated $70–$250 (industry estimate).
When to call a professional
- • Any burning smell, smoke, or water near electrical — stop and follow the safety steps.
- • Suspected low refrigerant, a compressor that won't start, or repeated breaker trips.
- • The coil keeps re-freezing after you've thawed it and changed the filter.
Common questions
- Why is ice forming on my AC line?
- Usually restricted airflow (dirty filter, closed vents) or low refrigerant. Thaw it with fan-only mode and change the filter; if it re-freezes, it likely needs a tech to check the charge.
- Should I add refrigerant myself?
- No. Low refrigerant means a leak, and refrigerant handling is licensed and regulated. Adding it without fixing the leak wastes money and can damage the system.
Sources
- Inspect central AC/furnace filters monthly; replace 1-inch filters every 1–3 months and thicker media filters every 6–12 months. Tier 1 (official)
ENERGY STAR (EPA/DOE) · verified 2026-07-26 - HVAC service call / diagnostic: $70–$250 (US, industry estimate). Tier 3 (industry estimate)estimate · has commercial bias
Angi · verified 2026-07-26