Outside Ac Unit Hums But Won T Turn On

Introduction

An air conditioner that hums but doesn’t start is a common and frustrating problem for homeowners. The humming sound usually indicates that the unit is trying to start, but something is preventing it from doing so. This issue often occurs during the hottest days of summer when you need your AC the most. Addressing this problem promptly is crucial to prevent further damage to your system and avoid sweltering in the heat.

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

Here are some of the most frequent reasons why your outside AC unit might be humming but not turning on:

Faulty Capacitor: The capacitor helps start the motor. A weak or failed capacitor is a prime suspect.
Dirty Condenser Coils: Dirt and debris restrict airflow, causing the unit to overheat and fail to start.
Locked Rotor Motor: The motor might be seized due to lack of lubrication or internal damage.
Overload Protector Tripped: An overload protector shuts down the motor to prevent damage from overheating.
Refrigerant Issues: Low refrigerant levels can cause the compressor to work harder and eventually fail to start.
Electrical Problems: Loose wiring, a tripped breaker, or a faulty contactor can prevent the unit from getting power.
Debris Obstruction: Leaves, branches, or other debris may be blocking the fan or other moving parts.
Bad Contactor: The contactor is an electrical switch that supplies power to the unit. It can fail over time.

Symptoms Checklist

Here are some symptoms that will help you accurately diagnose the problem:

The outside unit hums when the thermostat calls for cooling.
The fan on the outside unit does not spin.
The compressor does not start.
You hear a clicking sound from the unit.
Your circuit breaker for the AC unit has tripped.
The air coming from your indoor vents is warm or not as cold as usual.

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

Follow these steps to troubleshoot your AC unit:

Safety First: Turn off the power to the AC unit at the breaker box. This is crucial to prevent electrical shock.
Inspect the Disconnect Switch: Located near the outdoor unit, make sure the disconnect switch is in the “on” position. If it’s tripped or off, turn it back on.
Check the Circuit Breaker: Go to your electrical panel and ensure the breaker for the AC unit hasn’t tripped. If it has, reset it.
Clean the Condenser Coils: Use a garden hose (with a gentle spray nozzle) to clean the outside condenser coils. Remove any dirt, leaves, or debris. Be gentle to avoid bending the fins.
Remove Debris: Clear any leaves, branches, or other obstructions around the unit. Ensure nothing is blocking the fan.
Inspect the Capacitor: After turning off the power, carefully inspect the capacitor (usually a cylindrical component inside the unit). Look for bulging, leaking, or other signs of damage. Important: Do not touch the terminals on the capacitor, as they can store a dangerous electrical charge even after the power is off.
Check the Contactor: Look at the contactor (an electrical relay switch). If it is burnt or broken it might be the reason the compressor wont start.
Reset the Overload Protector: Some units have a reset button on the overload protector (located on or near the compressor). Allow the unit to cool down for a few hours, then try pressing the reset button.
Check Wiring Connections: After turning off the power, inspect the wiring connections inside the unit. Look for loose or corroded wires.
Listen Carefully: After turning the power back on, listen carefully for any unusual noises coming from the unit.
Wait and Observe: After completing the steps above, give the unit some time to start up (about 30 minutes).

Fix the Issue Without Buying Parts

Sometimes, you can resolve the issue without immediately resorting to replacements:

Reset the System: Simply turning off the power to the unit for 30 minutes and then turning it back on can sometimes reset the system and resolve the problem.
Thorough Cleaning: A dirty condenser coil is a common culprit. Ensure the coils are thoroughly cleaned of all debris.
Check for Obstructions: Ensure nothing is blocking the fan or any other moving parts.
Basic Maintenance: Regular cleaning and inspections can prevent future issues.

When Replacement Might Be Necessary

If the above steps don’t resolve the issue, a part may need replacing:

Capacitor: A faulty capacitor is a common replacement. The cost can range from $50 to $200 (USD) for the part and labor.
Contactor: Replacement cost is roughly $75-$250, including labor.
Fan Motor: If the fan motor is damaged, replacement can range from $150 to $500 (USD) including the service.
Compressor: Replacing the compressor is a major repair, costing anywhere from $800 to $2500 (USD).

Safety Warning

Always turn off the power to the AC unit at the breaker box before performing any maintenance or repairs.
Be extremely careful when working with electrical components. If you are not comfortable working with electricity, call a qualified technician.
Avoid working on the unit during wet conditions.
Do not touch any internal components while the power is on.

Tools You May Need

Screwdriver (Phillips and flathead)
Garden hose with spray nozzle
Work gloves
Multimeter (optional, for testing voltage – only for experienced users)

FAQ

Here are some frequently asked questions:

Q: Why is my AC humming but not blowing cold air? A: This often indicates a problem with the compressor or capacitor.
Q: How do I know if my capacitor is bad? A: Look for bulging, leaking, or other signs of physical damage. If you are skilled with a multimeter it can be tested, but this requires special training.
Q: Can I replace the capacitor myself? A: While it’s possible, it’s recommended to hire a professional due to the risk of electrical shock and the danger of the stored electrical charge in a capacitor.
Q: How often should I clean my AC unit’s condenser coils? A: At least once a year, ideally before the start of the cooling season.

Conclusion

Troubleshooting an AC unit that hums but won’t turn on can seem daunting, but by following these steps, you can often identify and resolve the issue yourself. Always prioritize safety and remember that it’s okay to call a qualified technician if you’re uncomfortable or unsure about any of the steps. Don’t give up immediately, try these tips first!