Your AC outside unit might not be turning off due to several potential malfunctions affecting different system components. Here's a breakdown of the most common reasons:
Potential Causes for AC Unit Running Continuously
The following issues can prevent your AC's outside unit (also called the condenser) from shutting off:
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Faulty Thermostat: A malfunctioning thermostat might not be sending the correct signal to turn off the AC unit. The thermostat could be improperly calibrated, have a faulty sensor, or be wired incorrectly.
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Frozen Evaporator Coil: If the evaporator coil (located inside the indoor unit) freezes, it can restrict airflow and cause the AC to run continuously in an attempt to cool the house. This can happen due to low refrigerant levels, a dirty air filter, or a blocked duct.
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Dirty Condenser Coil: A dirty condenser coil (located in the outside unit) impairs the unit's ability to dissipate heat. This forces the AC to work harder and run longer, potentially never turning off.
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Faulty Electrical Relay Switch: The relay switch controls the power to the compressor and fan motor in the outside unit. If this switch is stuck in the "on" position, it will keep the unit running even when it should be off.
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Constantly Blowing Fan: While the condenser fan often runs independently of the compressor, a wiring issue or relay problem could cause it to run constantly. This can be normal in some systems for a short period, but constant running usually indicates a problem.
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Low Refrigerant: Low refrigerant levels can cause the AC to struggle to cool the air effectively. As a result, the unit will run continuously in an attempt to reach the set temperature.
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Clogged Air Filter: A dirty air filter restricts airflow to the evaporator coil, causing it to potentially freeze and leading to the AC running non-stop.
Troubleshooting Steps
Before calling a professional, consider these steps:
- Check the Thermostat: Ensure it's set to "Cool" and the temperature is set lower than the current room temperature. Try turning the thermostat to "Off" or "Auto" to see if the outside unit shuts down.
- Replace the Air Filter: A clogged air filter is a common cause. Replace it with a clean one.
- Inspect the Outside Unit: Check for any visible debris or obstructions around the condenser coil.
- Allow Time for Defrosting: If you suspect a frozen evaporator coil, turn off the AC completely for several hours to allow the coil to thaw.
When to Call a Professional
If you've tried these troubleshooting steps and your AC unit is still not turning off, it's best to contact a qualified HVAC technician. Issues like low refrigerant or a faulty electrical relay switch require professional diagnosis and repair. Trying to fix these issues yourself can be dangerous and may void your warranty.
