Outside Ac Unit Hums But Doesn T Turn On

Introduction

Is your air conditioner making a humming noise but refusing to turn on? This is a common and frustrating problem that many homeowners face, especially during the hottest months. When your AC unit hums but doesn’t start, it means some component is trying to engage, but something is preventing the unit from running properly. This issue needs attention quickly. Without a functioning AC, your home can become unbearably hot, potentially causing discomfort and health risks, especially for the elderly or those with pre-existing conditions. Ignoring this problem can also lead to more serious and expensive repairs down the line.

Common Causes of outside ac unit hums but doesn t turn on

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

• Faulty Capacitor: The capacitor helps start the motor. If it’s weak or failing, the motor might hum but not kick on.
• Dirty Condenser Coils: Dirty coils reduce the AC’s ability to release heat, causing it to overheat and potentially prevent starting.
• Frozen Evaporator Coil: Restricted airflow can cause the evaporator coil inside your home to freeze, triggering a safety shut-off.
• Bad Contactor: The contactor is an electrical switch that sends power to the compressor. A bad contactor can prevent the compressor from starting.
• Overload Protector Tripped: The overload protector safeguards the compressor from overheating. If tripped, it cuts power to the unit.
• Locked Rotor: The motor itself might be seized or obstructed, preventing it from turning.
• Low Voltage: Insufficient voltage supply can prevent the motor from starting, causing a hum.
• Refrigerant Leak: Low refrigerant can cause the compressor to work harder and potentially overheat, leading to a shutdown.
• Blocked Fan Motor: If the fan motor is obstructed, the unit can overheat preventing proper operation.

Symptoms Checklist

Check for these symptoms to help pinpoint the problem:

• Humming noise coming from the outdoor unit.
• Fan not spinning.
• Circuit breaker tripping repeatedly.
• Warm air blowing from vents inside the house.
• Ice buildup on the refrigerant lines or the outdoor unit.
• The unit turns on and off quickly (short cycling).
• No sound at all from the outdoor unit except the hum.

How to Fix outside ac unit hums but doesn t turn on Step-by-Step Guide

Follow these steps to troubleshoot your AC unit:

1. Turn Off the Power: Go to your circuit breaker box and turn off the breaker that supplies power to the outdoor AC unit. This is crucial for your safety.
2. Inspect the Condenser Coils: Look at the outdoor unit’s coils. Are they covered in dirt, leaves, or debris? If so, proceed to step 3.
3. Clean the Coils: Use a garden hose (with a gentle spray nozzle) to wash the coils from the inside out. Avoid using high pressure, which can damage the fins.
4. Check the Fan: Make sure the fan blades are free from obstructions like twigs or leaves. Gently try to spin the fan blades with your hand (power off!). If they don’t move freely, something might be blocking them.
5. Inspect the Capacitor: (If you are comfortable) Open the service panel on the side of the unit. Locate the capacitor (it’s a cylindrical component). Look for signs of bulging, leaking, or corrosion. If you notice any of these, it’s likely the capacitor is failing. Warning Capacitors can store an electrical charge.
6. Check the Contactor: The contactor is a switch with several wires attached. Look to see if any of the wires are loose or burnt.
7. Check the Overload Protector: The overload protector is a reset switch. If you can find this button push it in firmly to see if the unit starts.
8. Check for Ice Buildup: Inspect the refrigerant lines entering the outdoor unit. If you see ice, the evaporator coil inside your home might be frozen.
9. Thaw a Frozen Evaporator Coil: If you suspect a frozen coil, turn the AC off and set the thermostat fan to “ON” to circulate air and melt the ice. This can take several hours. Also check your air filter and replace it if dirty.
10. Check the Air Filter: A dirty air filter restricts airflow and can cause the evaporator coil to freeze. Replace it with a clean filter.
11. Reset the Breaker: After allowing the unit to sit for at least 30 minutes (especially if you suspect a frozen coil), turn the circuit breaker back on.
12. Monitor the Unit: Turn the AC back on and observe its behavior. Does it start normally? If it still hums but doesn’t start, proceed to the next steps.
13. Voltage Test: Using a multimeter test the voltage coming to the unit. Compare it with the specifications. If it is low call an electrician.

Fix the Issue Without Buying Parts

Before considering replacement parts, try these free fixes:

• Reset: A simple reset by turning off the breaker and turning it back on after a few minutes can sometimes resolve minor electrical glitches.
• Cleaning: Regularly cleaning the condenser coils and removing debris ensures efficient operation.
• Inspection Tips: Routinely inspect the unit for any visible damage, loose connections, or signs of leaks.
• Maintenance Basics: Change your air filter monthly, especially during peak usage periods. Ensure proper airflow around the outdoor unit.

When Replacement Might Be Necessary

If the humming persists after trying the above steps, a component might need replacing. Common culprits include:

• Capacitor: Replacing a capacitor usually costs between $100 and $300.
• Contactor: Replacing a contactor can cost between $150 and $350.
• Compressor: Compressor replacement is a major repair, costing anywhere from $800 to $2500 or more. This often warrants considering a new AC unit altogether.

Safety Warning

• Always turn off the power to the AC unit at the circuit breaker before performing any maintenance or inspections.
• Avoid working on electrical components if you are not comfortable or experienced. Contact a qualified technician.
• Never use water near electrical components unless the power is off.
• Be cautious of sharp edges on the unit’s metal housing.

Tools You May Need

• Screwdriver (various types)
• Garden hose with a spray nozzle
• Soft brush or fin comb
• Multimeter (for testing voltage – optional and requires experience)
• Gloves
• Safety glasses

FAQ

Q: Why is my AC humming even after I cleaned the coils?
A: The humming could be due to a failing capacitor or contactor, even with clean coils. For more related activities, check out our My Window Unit Air Conditioner Is Leaking Water.

Q: How do I know if my capacitor is bad?
A: Look for signs of bulging, leaking, or corrosion on the capacitor. Use a multimeter to test it.

Q: What if my AC starts but then quickly shuts off?
A: This could be a sign of a tripped overload protector or a failing compressor.

Q: Can I replace the capacitor myself?
A: Replacing a capacitor can be dangerous, since the component can store a high-voltage electrical charge. Consider hiring a professional.

Conclusion

Troubleshooting a humming AC unit can seem daunting, but by following these steps, you can often identify and resolve the issue yourself. Start with the simple checks, such as cleaning and filter replacement. If the problem persists and involves electrical components you’re not comfortable with, it’s best to call a qualified HVAC technician. Addressing the problem early can save you from more extensive and expensive repairs in the future.

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