Outside Ac Unit Humming But Not Turning On

Introduction

Is your air conditioner humming loudly but failing to kick on? This is a common and frustrating problem, especially during sweltering weather. When your outside AC unit hums but doesn’t turn on, it indicates a potential issue that needs attention. Ignoring it can lead to further damage to your AC system, higher energy bills, and a very uncomfortable home. It’s crucial to address this problem quickly to avoid expensive repairs or even complete unit replacement.

Common Causes of Outside AC Unit Humming But Not Turning On

Here are some common reasons why your outside AC unit might be humming without starting:

Faulty Capacitor: The capacitor is like a battery that gives the motor the initial jolt to start. If it’s weak or damaged, the motor might only hum.
Dirty Condenser Coils: Over time, dirt, leaves, and debris can accumulate on the coils, restricting airflow and causing the unit to overheat and fail to start.
Locked Rotor Motor: This happens when the motor’s rotor is physically stuck, preventing it from turning.
Worn Contactor: The contactor is a switch that sends power to the AC unit. If it’s worn or damaged, it might fail to deliver the necessary electricity.
Overload Protection: The overload protector trips when the motor is overheating, shutting down the unit to prevent damage.
Low Voltage: Insufficient voltage supply to the unit can prevent it from starting, leading to a humming sound.
Refrigerant Issues: Although less common in this particular scenario, very low refrigerant can sometimes prevent the compressor from starting.
Frozen Evaporator Coil: If the evaporator coil (inside the house) is frozen, it can affect the outdoor unit’s ability to start.

Symptoms Checklist

Here are some indicators to help you pinpoint the problem:

The outdoor unit is humming loudly.
The fan on the outdoor unit is not spinning.
The compressor is not running.
The circuit breaker for the AC unit may be tripped.
The air coming from your vents is warm.
You hear clicking sounds from the outdoor unit before it hums.

How to Fix Outside AC Unit Humming But Not Turning On Step-by-Step Guide

Follow these steps to troubleshoot and potentially fix the problem:

Safety First: Turn off the power to the AC unit at the breaker box. This is crucial to avoid electrical shock.
Inspect the Breaker: Check the circuit breaker for the AC unit. If it’s tripped, reset it. If it trips again immediately, there’s a more serious problem.
Clean the Condenser Coils: Use a garden hose (with a gentle spray nozzle) to clean the outside of the condenser coils. Remove any visible dirt, leaves, or debris.
Inspect the Fan Blades: Make sure the fan blades are free of obstructions and can spin freely. Remove any twigs or debris that might be blocking them.
Check the Capacitor (Visually): Locate the capacitor (usually a cylindrical metal component) inside the control panel of the outdoor unit. Look for signs of bulging, leaking, or damage. Do not touch the capacitor unless you are a qualified technician as it can hold a dangerous electrical charge even after the power is turned off.
Check the Contactor: The contactor is a switch that allows power to flow to the compressor. Check if the contactor is burned, broken or pitted. If it is, this is a common failure point.
Check for Frozen Evaporator Coils (Indoor Unit): If the evaporator coil inside your house is frozen, it can prevent the outdoor unit from starting. Inspect it and allow it to thaw completely.
Check Air Filter (Indoor Unit): A dirty air filter restricts airflow, which can cause the evaporator coil to freeze. Replace the air filter with a clean one.
Reset the AC Unit: Some AC units have a reset button. Check the unit’s manual or look for a small red button on the control panel. Press it to reset the unit.
Check Voltage: Use a multimeter to ensure the proper voltage is supplied to the AC unit. If the voltage is too low, it could be the cause of the problem. (Consult a qualified electrician for this step if you are not comfortable working with electricity).
Wait and Try Again: After cleaning and inspecting the unit, wait for about 30 minutes before turning the power back on and trying to start the AC.
Listen Carefully: When you turn the power back on, listen carefully for any unusual noises from the unit. This can help you identify the source of the problem.

Fix the Issue Without Buying Parts

Sometimes, you can resolve the issue without immediately buying replacement parts. Here are some free methods:

Reset the System: As mentioned above, try resetting the AC unit.
Thorough Cleaning: Ensure the condenser coils and fan blades are completely clean and free of debris.
Inspect Wiring: Look for any loose or corroded wiring connections.
Proper Ventilation: Make sure the outdoor unit has adequate ventilation. Don’t block it with plants or other objects.
Regular Maintenance: Schedule annual AC maintenance to prevent future problems.

When Replacement Might Be Necessary

If you’ve tried all the troubleshooting steps and the AC unit still hums but doesn’t start, replacement of components or the entire unit might be necessary. A faulty capacitor or contactor often need to be replaced by a professional. If the compressor is failing, it’s generally more cost-effective to replace the entire outdoor unit. Capacitor replacement can range from $100-$300, contactor replacement can range from $150- $350. Outdoor unit replacement can cost $2,000-$5,000, depending on the size and efficiency.

Safety Warning

Always turn off the power to the AC unit at the breaker box before performing any maintenance or repairs.
Avoid touching any electrical components, especially the capacitor, as it can hold a dangerous electrical charge.
Be careful when using a garden hose to clean the condenser coils to avoid spraying water on electrical components.
If you are not comfortable working with electricity or mechanical components, contact a qualified HVAC technician.

Tools You May Need

Here’s a list of tools you might find helpful:

Screwdriver (Phillips and flathead)
Garden hose with a spray nozzle
Multimeter (for checking voltage – use with extreme caution)
Wrench set
Work gloves

FAQ

Here are some frequently asked questions:

Q: Why is my AC unit humming even after I cleaned the coils? A: The humming could be due to a faulty capacitor or a locked rotor motor. These issues often require professional attention.
Q: How do I know if the capacitor is bad? A: Visually inspect the capacitor for bulging or leaking. However, a professional technician can test the capacitor’s capacitance using a multimeter to be sure.
Q: Can I replace the capacitor myself? A: Replacing a capacitor can be dangerous if you are not familiar with electrical work. It’s best to hire a qualified HVAC technician to do it safely.
Q: How often should I clean my AC unit? A: Clean the condenser coils at least once a year, or more often if you live in a dusty or pollen-rich environment.

Conclusion

Having your outside AC unit humming but not turning on can be a stressful experience. By following these troubleshooting steps, you may be able to identify and resolve the issue yourself. However, if you’re uncomfortable working with electricity or mechanical components, or if the problem persists, don’t hesitate to call a qualified HVAC technician. Addressing the problem promptly can save you money on costly repairs and ensure your home stays cool and comfortable.