AC Not Turning Off When Temp Reached

Quick answer

If your AC runs continuously after reaching the set temperature, check the thermostat settings, clean the air filter, and ensure the thermostat is properly calibrated. If the issue persists, the thermostat or control board may need replacement.

Confirm the symptom

• AC runs nonstop even after reaching set temperature
• Thermostat shows correct temperature but AC doesn't shut off
• Room feels comfortable but AC keeps running
• No error codes on thermostat or AC unit

Tools and prep

• Screwdriver
• New air filter (if needed)
• Multimeter (optional)
• Safety gloves
• Turn off AC power at the thermostat or circuit breaker before starting
• Check if the area around the thermostat is free of drafts or heat sources

Step-by-step troubleshooting

1. Check Thermostat Settings
   Do: Verify the thermostat is set to 'Cool' mode and the temperature is higher than the current room temperature.
   Observe: Thermostat settings are correct but AC still runs.
   Means: Settings are not the issue; move to next step.
   Next: Clean or Replace Air Filter
2. Clean or Replace Air Filter
   Do: Remove the air filter and clean it if reusable, or replace it with a new one.
   Observe: AC runs normally after replacing the filter.
   Means: Dirty filter was causing airflow issues.
   Next: Done
3. Check Thermostat Calibration
   Do: Use a separate thermometer to compare the thermostat's reading with the actual room temperature.
   Observe: Thermostat reads significantly different from the actual temperature.
   Means: Thermostat is inaccurate and needs recalibration or replacement.
   Next: Calibrate or Replace Thermostat
4. Calibrate or Replace Thermostat
   Do: Follow the manufacturer's instructions to calibrate the thermostat. If it's a programmable thermostat, consider replacing it with a new one.
   Observe: Thermostat now accurately reflects the room temperature and controls the AC correctly.
   Means: Thermostat was the issue.
   Next: Done
5. Inspect for Obstructions
   Do: Check for any obstructions in the ductwork or around the AC unit that might be affecting airflow.
   Observe: Obstructions are found and removed.
   Means: Obstructions were causing airflow issues.
   Next: Done
6. Check for Refrigerant Leaks
   Do: Listen for hissing sounds and check for ice buildup on the refrigerant lines. Use a refrigerant leak detector if available.
   Observe: Leak detected or ice buildup present.
   Means: Refrigerant leak is causing the issue.
   Next: Call a Professional
7. Inspect Control Board
   Do: Check the control board for any visible signs of damage or burn marks.
   Observe: Damage or burn marks are found on the control board.
   Means: Control board is faulty and needs replacement.
   Next: Call a Professional

Common causes

Parts matching

Common parts needed to fix an AC that doesn't turn off when the temperature is reached:

• Air filter
• Thermostat
• Refrigerant (professional installation required)
• Control board
• Duct repair kit
• Fan motor

Always purchase parts compatible with your specific AC model. Check the manufacturer's website for specifications.

When to call a professional

• If you detect a refrigerant leak or ice buildup on the refrigerant lines
• If the control board shows signs of damage or burn marks
• If the AC still doesn't turn off after replacing the air filter and checking thermostat settings
• If you're unsure about handling electrical components or refrigerant
• If the issue persists after following all troubleshooting steps

FAQ

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