Troubleshooting Guide: What to Do If Your Wall AC Isn’t Cooling (or Heating)
Intro: Don’t Panic—Start Simple
Few things feel worse than flipping on your wall AC during a heatwave and realizing... nothing’s happening. Or worse, it’s running but blowing warm air.
The good news? Most issues aren’t major breakdowns—they’re small maintenance hiccups you can fix in minutes.
I’ve been called out for hundreds of “broken” through-the-wall units over the years, and nine times out of ten, the fix was a dirty filter, blocked vent, or loose connection.
So before you call for service, run through this checklist. You might save yourself time, money, and a sweaty afternoon.
1. Check the Power First
It sounds obvious, but you’d be surprised how often the issue is electrical.
Do this:
✅ Make sure the unit is plugged in securely.
✅ Inspect the power cord for damage or scorch marks.
✅ Check the circuit breaker — if it’s tripped, reset it once.
✅ Test the outlet by plugging in another device.
If you’re running a 230V model (like the GE 12,000 BTU AJEQ12DWJ), confirm it’s on a dedicated circuit. These larger units can overload standard household plugs.
Jake’s tip: “No power? Don’t immediately assume it’s the AC—half the time it’s the outlet or breaker.”
2. Clean or Replace the Filter
If your unit has power but the airflow feels weak or warm, your filter is the next suspect.
A clogged filter chokes airflow, forcing the system to run longer, overheat, or even freeze up.
Fix it:
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Open the front grille.
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Remove the filter.
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Rinse with warm water and mild soap.
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Let dry fully before reinstalling.
Clean it monthly during cooling season. You’ll feel the difference in minutes.
3. Inspect Airflow and Vents
Your through-the-wall AC needs clear intake and exhaust paths. Any blockage—inside or outside—kills efficiency.
Check for:
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Furniture blocking the front grille.
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Curtains or shelves near the air outlet.
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Leaves, lint, or debris clogging the rear vent outside.
Clean both sides gently with a brush or vacuum.
If you hear airflow but still feel warm air, move to the next step.
4. Verify the Thermostat Settings
You’d be amazed how often settings get nudged accidentally.
Double-check that:
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The mode is set to Cool, not Fan or Energy Saver.
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Temperature is lower than room temperature.
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The fan speed isn’t set to “Low” during peak heat.
If your thermostat display is flashing or blank, replace the batteries in the remote or reset the control panel using the reset button (if available).
Jake’s advice: “Digital thermostats are great—until someone bumps the remote and turns on ‘Fan Only.’ Always check the mode first.”
5. Look for Ice or Frost on the Coils
If your unit runs but doesn’t cool well, open the front panel and inspect the evaporator coil (the metal fins behind the filter).
If it’s covered in frost, the coil has frozen due to:
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Low airflow (dirty filter)
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Blocked vents
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Running in cool weather (below 60°F)
Fix:
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Turn the unit off.
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Let it thaw completely (2–4 hours).
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Clean the filter and restart on Fan mode for 15 minutes.
Once airflow improves, the problem usually disappears.
6. Clear the Drain Line
If your unit leaks water indoors or starts cycling off unexpectedly, the condensate drain may be clogged.
Check the small drain hole at the bottom of the wall sleeve (outside). Use a thin wire, straw, or pipe cleaner to remove buildup.
Ensure the sleeve tilts slightly downward toward the exterior so water flows out naturally.
If your drain line smells musty, flush it with a mix of vinegar and warm water to kill mold.
7. Reset the Unit
Modern through-the-wall ACs include safety sensors and surge protectors that can trip during storms or voltage spikes.
If your unit suddenly stops working:
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Unplug it for 60 seconds.
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Plug back in.
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Press the Reset button (if your model has one).
If it restarts normally, you just cleared a simple control lockout.
8. Check for Unusual Sounds
Every sound tells a story:
| Sound | What It Means | Fix |
|---|---|---|
| Rattling | Loose panel or fan blade | Tighten screws, clear debris |
| Buzzing | Electrical vibration | Check outlet & plug |
| Clicking | Relay switching or mode change | Normal |
| Grinding | Worn fan motor | Call a technician |
If the noise started suddenly, shut it off and inspect for small debris caught near the fan.
9. Test Heating Function (If Equipped)
If your model includes electric heat or a heat pump, warm air problems are often thermostat- or voltage-related.
Check:
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Heat mode is active, not Fan.
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For 230V models, confirm full power is reaching the outlet.
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Clean coils—dust reduces heating efficiency.
If it still blows cold, the heat strip or reversing valve may need professional service.
10. Eliminate Odors and Musty Air
If your AC smells stale or moldy, moisture and dust are sitting inside.
Fix it fast:
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Mix equal parts vinegar and water.
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Spray coils and interior surfaces.
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Wipe clean with a soft cloth.
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Run the unit in Fan mode for 30 minutes to dry.
Drop an AC pan tablet in the drain pan monthly to prevent mold and algae.
Jake’s tip: “If your AC smells like wet socks, it’s begging for a cleaning.”
11. Check the Room Size
Sometimes the problem isn’t the unit—it’s the space.
If your room’s square footage exceeds the unit’s rated capacity, the AC simply can’t keep up.
Quick guide:
| Room Size | BTUs Needed |
|---|---|
| 150–250 sq. ft. | 6,000 BTUs |
| 250–350 sq. ft. | 8,000–9,000 BTUs |
| 350–550 sq. ft. | 10,000–12,000 BTUs |
If your room is sun-facing, has high ceilings, or poor insulation, you might need a larger model or additional unit.
👉 See Jake’s full guide: How to Size a Through-the-Wall AC
12. Know When to Call a Pro
You’ve cleaned, checked, and reset—but it’s still not cooling or heating. That’s when it’s time for professional help.
Call an HVAC technician if you notice:
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Compressor hums but never starts.
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Air feels warm even after coil cleaning.
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Electrical burning smell.
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Unit trips breaker repeatedly.
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Visible rust or refrigerant oil on coils.
These point to electrical, refrigerant, or motor issues that need tools and training to repair safely.
Jake’s advice: “If you need to open a sealed panel or deal with wiring—stop. That’s your cue to call in the pros.”
13. Prevent Problems Before They Start
The best troubleshooting plan is prevention. Keep your AC healthy with Jake’s 10-minute monthly routine:
✅ Clean filter
✅ Check outdoor vent for debris
✅ Clear drain hole
✅ Inspect seals for leaks
✅ Listen for new noises
✅ Wipe down front grille
These quick steps keep 90% of issues from ever happening.
Final Thoughts: Stay Cool, Stay Proactive
A through-the-wall AC is one of the most reliable cooling systems you can own. When it acts up, the fix is often simple—cleaning a filter, clearing a drain, or resetting controls.
Take a few minutes to inspect it before you call for help. You’ll often find the problem—and the solution—yourself.
Jake’s rule: “If your wall unit stops cooling, don’t assume the worst. Start with the easy stuff—you’ll be surprised how often that’s all it takes.”
In the next Blog we will learn more about Can a Wall Unit Cool Multiple Rooms?
