Your AC is running. You can hear it. But your house is still hot. Before you call a tech and spend $150+ on a service call, there are several things worth checking yourself — some of them fix the problem instantly.
Check 1: Your Air Filter
This is the single most common reason an AC stops cooling properly. A clogged filter chokes off airflow to the evaporator coil, which can cause the coil to freeze solid. When that happens, your AC runs but pushes warm air.
Pull the filter out. Hold it up to a light. If you cannot see through it, that is your problem. Replace it and give the system a few hours to recover.
How often to change it: every 1-3 months during cooling season, more often if you have pets.
- AC air filters (multi-pack) — keep spares on hand
Check 2: Your Thermostat
Verify these settings:
- Mode is set to COOL (not HEAT or FAN ONLY)
- Temperature is set lower than the current room temperature
- Fan is set to AUTO (not ON — the ON setting runs the fan continuously, which can feel like warm air between cooling cycles)
If you have a battery-powered thermostat, replace the batteries. Dead batteries cause erratic behavior.
- Smart thermostat — upgrade from an old manual unit
Check 3: The Circuit Breaker
Your AC has two breakers — one for the indoor unit (air handler) and one for the outdoor unit (condenser). If the outdoor breaker tripped, the fan runs inside but no cooling happens because the compressor is off.
Check your electrical panel and flip any tripped breakers off, then back on.
Check 4: The Outdoor Unit
Go outside and look at your condenser unit:
- Is it running? You should hear the fan and compressor.
- Is it covered in debris, leaves, or grass clippings? A dirty condenser cannot release heat properly.
- Are the fins bent or clogged? Restricted airflow reduces cooling capacity.
If it is dirty, turn the system off and gently hose it down from the inside out. Do not use a pressure washer.
- AC condenser coil cleaner — spray on, hose off
- AC fin comb — straighten bent fins to restore airflow
Check 5: Ice on the Unit
If you see ice forming on the refrigerant lines, the outdoor unit, or the indoor coil, your system is freezing up. This is caused by restricted airflow (dirty filter), low refrigerant, or a blower fan problem.
What to do: turn the AC off but leave the fan set to ON. Let the ice melt completely — this can take several hours. Replace the filter. Then try turning the AC back on. If it freezes again, you need a tech.
Check 6: Vents and Registers
Walk through every room. Make sure all supply vents are open and not blocked by furniture, curtains, or rugs. Closed or blocked vents restrict airflow and can cause the system to struggle.
Also check the return air vents — these are usually larger grilles on walls or ceilings. They need clear space to pull air back to the system.
When to Call a Pro
If you have checked everything above and your AC is still not cooling, the problem is likely:
- Low refrigerant (requires a licensed tech to diagnose and recharge)
- A failed compressor
- An electrical component failure (capacitor, contactor, control board)
- Ductwork leaks losing cooled air into walls or attics
These all require professional equipment and expertise to fix safely.
Getting Help in Pittsburgh
If your AC is not cooling and the DIY checks did not solve it, get connected with a local HVAC pro through KeepYinzCool. We will find yinz someone who can diagnose and fix it — often same-day.