Troubleshooting Guide: What to Do If Your Wall AC Isn’t Cooling (or He

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Through-the-wall air conditioners offer reliable climate control — but when something goes wrong, they can leave you sweating or shivering. Whether your wall unit is blowing warm air in summer, refusing to heat in winter, or doing nothing at all, this guide walks you through practical, step-by-step solutions before you pick up the phone to call for service.

Let’s help Samantha (and you) troubleshoot with confidence.

🔧 Quick First Check: Is It a Basic Power or Setting Issue?

Before diving into components and diagnostics, rule out the simple stuff:

✅ 1. Is It Plugged In and Turned On?

Check that the unit is securely plugged into the wall.
Some wall ACs (especially older GE and Hotpoint models) have resettable power plugs — hit the reset button.

✅ 2. Thermostat Settings

Cooling mode: Make sure the unit is in “Cool” mode and the temperature is set lower than the current room temp.
Heating mode (if combo unit): Ensure it’s in “Heat” mode and not “Fan Only.”
Confirm the remote’s batteries aren’t dead and that it’s set to the correct mode.

✅ 3. Check the Circuit Breaker

If the breaker tripped, reset it.
Frequent trips may indicate a short or compressor issue.

🌬️ Problem 1: Wall AC Isn’t Cooling

If your unit runs but the air isn’t cold, here’s what might be happening.

🔍 A. Dirty Air Filter or Blocked Airflow

Symptoms: Weak airflow or room doesn’t cool down.
Fix: Remove the front panel and wash or replace the air filter.
Clogged filters cause the evaporator coil to freeze, limiting cooling performance.

✅ Samantha’s Tip: Set a reminder every 30 days during summer to clean your filter.

🔍 B. Ice on the Coils

Symptoms: Frost or ice visible behind the front grill.
Fix:
- Turn the unit off and let it thaw for a few hours.
- Once thawed, clean the filter and ensure vents are open and unblocked.
- Avoid running the unit with windows or doors open — it stresses the coil.

🔍 C. Low Refrigerant or Leak

Symptoms: Constant running but no real cooling.
Fix: This requires a licensed HVAC pro. R-410A and R-32 systems can’t be recharged without EPA certification.

🔍 D. Thermistor or Temperature Sensor Fault

A broken or misaligned sensor tells the unit the room is cooler than it is.
Fix: On some models (like LG), the sensor can be repositioned; others require professional replacement.

🔥 Problem 2: Wall AC Isn’t Heating

Not all through-the-wall units have heat. If yours does and it’s not working:

🔍 A. Heat Mode Not Engaged

Double-check remote settings and mode indicators.
Some Friedrich and Amana models need a few minutes to kick into heat mode.

🔍 B. Electric Heat Kit Not Working (Electric Units)

Symptoms: No warm air, just fan blowing.
Fix:
- Ensure the electric heat kit is installed and connected properly.
- Check for tripped internal limit switches or burned-out heating elements (a technician will need to test these).

🔍 C. Reversing Valve Stuck (Heat Pump Units)

Symptoms: Unit cools in winter or blows lukewarm air.
Fix: Heat pump units like GE Zoneline or LG may have a stuck reversing valve. A pro can test the solenoid and valve operation.

🔁 Problem 3: Wall Unit Keeps Turning On and Off (Short Cycling)

Short cycling can reduce the unit’s lifespan and drive up energy bills.

🔍 A. Oversized Unit

Too powerful for the space = rapid cooling = quick shutdown.
Fix: Consider switching to a properly sized model (see our BTU sizing guide).

🔍 B. Thermostat Placement

Mounted too close to the unit or in direct sun?
Fix: Adjust remote location or add shading to avoid false readings.

🔍 C. Dirty Evaporator or Condenser Coils

Fix: Clean the coils using a soft brush or coil cleaner spray.

🔇 Problem 4: AC Is On but No Air Is Coming Out

If you hear the compressor running but feel nothing at the vents:

🔍 A. Blower Fan Motor Failure

Check if the fan blade is spinning.
If not, the fan motor could be burned out or jammed.

🔍 B. Control Board or Relay Issue

Fix: On units like Friedrich, the PCB (printed circuit board) may fail and stop sending voltage to the fan motor. This repair requires a technician.