Why Your AC Isn't Cooling (And the Fixes You Can Do Yourself)
When the AC runs but the house won't cool, the cause is usually one of a few simple things. Here's how to troubleshoot it yourself before paying for a service call.
When the air conditioner is clearly running but the house just won't cool, it's frustrating — but the cause is usually one of a handful of simple things, and several are free to fix. Work through these in order before you book a service call.
Start with the easy wins
1. Check the thermostat. It sounds obvious, but set it to COOL, several degrees below the current room temperature, with the fan on AUTO (not ON — "ON" runs the fan without cooling and can feel like warm air). If the screen is blank, replace the batteries.
2. Replace the air filter. This is the single most common cause. A clogged HVAC filter strangles airflow, which kills cooling output and can freeze the coil solid. Swap in a clean one — see how to change a furnace filter (same filter for AC). Owner Tools schedules this as replace HVAC air filter.
3. Check power. Make sure the AC's breaker hasn't tripped and the outdoor disconnect switch (a small box near the condenser) is on. A repeatedly tripping AC breaker points to a deeper problem worth a pro.
Clear the outdoor unit
The outdoor condenser sheds your home's heat to the air. If it's choked with leaves, grass, or dirt, it can't — and the house stays warm.
- Turn off power at the disconnect.
- Clear leaves, grass clippings, and debris from around and inside the unit.
- Gently rinse the condenser coils with a hose (low pressure, top down) to wash off the grime.
- Make sure there's at least a couple of feet of clearance around it.
This is the clean the AC condenser coils task, and it makes a real difference in cooling on hot days.
Look for ice and water problems
- Iced-over coil or refrigerant line: if you see frost or ice on the indoor evaporator coil or the copper line, shut the system off and let it thaw fully (a few hours). Running it frozen can wreck the compressor. Then replace the filter and open all the vents. If it ices again, you likely have low refrigerant or a blower issue — call a pro.
- A clogged condensate line: many systems shut off cooling on purpose when the drain backs up, to prevent water damage. Clearing it can bring cooling right back — see clear the HVAC condensate drain line.
Check airflow inside
Walk the house and make sure supply vents are open and unblocked by furniture or rugs, and that return vents aren't covered. Closing too many vents actually strains the system and reduces cooling everywhere.
When to call a pro
If you've done all of the above and it still won't cool, the likely culprits need a technician:
- Low refrigerant — almost always means a leak; topping it off without fixing the leak is a temporary patch.
- A failing compressor or capacitor — the outdoor unit hums but the fan won't spin, or it trips the breaker.
- A dead blower motor — no air movement at the vents at all.
An annual professional HVAC tune-up catches most of these before summer, when a failure is both miserable and expensive. For the bigger picture, see the HVAC system overview and when to replace your system.
Make it automatic
Build your free Owner Tools plan and we'll schedule filter changes, coil cleaning, the condensate-line flush, and the yearly tune-up so your AC is ready before the first heat wave. No login, no address required.