Window AC Not Cooling — Causes and Fixes
When a window AC blows but the air is not cold, the cause is almost always airflow or a dirty unit — not a dead compressor. Work through these in order before replacing anything.
1. Clean or Replace the Filter
Pop off the front grille and pull the filter. A clogged filter is the most common reason a window unit stops cooling — it chokes airflow and can freeze the coil. Wash a reusable filter with warm soapy water, dry it fully, and reinstall.
2. Check for a Frozen Coil
If you see ice on the coils behind the filter, turn the unit to FAN only (no cooling) for an hour to melt it. A frozen coil is caused by restricted airflow (dirty filter), low refrigerant, or running the AC when it is too cold out. After it thaws, clean the filter and try cooling again.
3. Clean the Coils
Dust and grime on the front (evaporator) and rear (condenser) coils kill cooling. With the unit unplugged, vacuum the coils gently and use a coil cleaner spray. The rear coils especially collect dirt and bugs and need clearing once a season.
4. Check Placement and Seals
Make sure the unit is tilted slightly toward the outside for drainage, the side accordion panels seal the gaps, and it is not in direct afternoon sun. Warm air leaking in around the unit makes it run constantly without cooling the room.
When It Is Low on Refrigerant
If the coils are clean, the filter is fresh, and it still will not cool, the unit may have lost refrigerant charge. Window units are sealed systems — recharging is rarely cost-effective, so a unit more than ~8 years old is usually worth replacing.
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FAQ
Most often a clogged filter or frozen/dirty coils restricting airflow. Clean the filter and coils first, and thaw any ice by running fan-only for an hour.
Usually not worth it. Window units are sealed and recharging requires a pro; on an older unit, replacement is more economical.
Always unplug an appliance and shut off its water supply before servicing. This guide is informational and not a substitute for a qualified technician.