Window Unit Ac Compressor Won T Kick On

Introduction

A window unit AC that refuses to blow cold air is a common summer frustration. If your window AC unit turns on but the air remains warm, the problem likely lies with the compressor. The compressor is the heart of the cooling system, responsible for circulating the refrigerant. When it fails to start, your AC becomes nothing more than a fan. Addressing this quickly is important because continued operation without the compressor functioning can damage other components and waste electricity.

Common Causes of Window Unit AC Compressor Won’t Kick On

Here are several potential reasons why your window AC compressor might not be starting:

Overheating: Like any motor, the compressor can overheat and shut down to protect itself.
Dirty Air Filter: A clogged air filter restricts airflow, causing the unit to work harder and potentially overheat.
Frozen Coils: Restricted airflow or low refrigerant can cause the coils to freeze, preventing the compressor from starting.
Faulty Capacitor: The capacitor gives the compressor the initial jolt of energy it needs to start. A weak or failed capacitor is a common culprit.
Bad Compressor Relay: The relay switches power to the compressor. If it’s faulty, it won’t send power to the compressor.
Thermostat Issues: If the thermostat isn’t signaling for cooling, the compressor won’t turn on.
Low Refrigerant: While less common in window units, low refrigerant can prevent the compressor from engaging.
Power Supply Problems: Insufficient voltage or a tripped circuit breaker can prevent the compressor from receiving power.
Compressor Overload Protector: This safety device trips when the compressor gets too hot, shutting it down. It might need time to reset.

Symptoms Checklist

Confirm that the problem is indeed the compressor:

The AC unit powers on, but blows warm air.
You hear the fan running, but no humming or buzzing sound from the compressor.
The unit might make a clicking sound and then nothing.
The circuit breaker for the AC unit might trip frequently.
You notice ice forming on the cooling fins.

How to Fix Window Unit AC Compressor Won’t Kick On Step-by-Step Guide

Follow these steps to troubleshoot and potentially fix the problem:

Unplug the AC Unit: Safety first! Always unplug the unit from the power outlet before performing any maintenance or troubleshooting.
Check the Power Outlet: Make sure the outlet is working by plugging in another device. If the outlet isn’t working, check the circuit breaker.
Reset the Circuit Breaker: Locate the circuit breaker that controls the AC unit and ensure it hasn’t tripped. Reset it if necessary.
Clean the Air Filter: Remove the air filter and clean it thoroughly with soap and water. Let it dry completely before reinstalling. A dirty filter can choke the unit.
Inspect the Cooling Fins: Check the cooling fins (the metal coils) for dirt and debris. Gently clean them with a fin comb or a soft brush.
Allow Unit to Rest: If you suspect overheating, unplug the unit and let it sit for several hours to cool down completely. The overload protector might reset itself.
Check the Thermostat Setting: Make sure the thermostat is set to a temperature lower than the current room temperature and that it’s in “cool” mode.
Listen for Humming: After waiting, plug the unit back in and listen carefully. If you hear a faint humming sound but the compressor doesn’t start, the capacitor might be the problem.
Check the Capacitor (Advanced – Requires Caution): Warning: Capacitors can hold an electrical charge even when the unit is unplugged. If you are not comfortable working with electricity, skip this step and consult a professional. Carefully discharge the capacitor using an insulated screwdriver before touching it. Inspect the capacitor for bulging, leaking, or other signs of damage.
Clean the Exterior: Make sure that nothing is blocking airflow to or from the outside of the unit.
Ensure Proper Ventilation: Make sure that the room isn’t closed off. If the room is too small the unit might overheat.

Fix the Issue Without Buying Parts

Here are a few things you can try before considering replacement parts:

Reset: Unplug the unit for an extended period (overnight) to allow all components to fully discharge and reset.
Cleaning: Thoroughly clean the air filter and coils. This improves airflow and reduces stress on the compressor.
Location: Consider the unit’s location. Direct sunlight can cause overheating. Improve shading if possible.
Ventilation: Make sure the room has adequate ventilation, preventing the unit from overworking.
Inspection: Carefully examine all wiring connections for looseness or corrosion.

When Replacement Might Be Necessary

If the troubleshooting steps above don’t solve the problem, and especially if you suspect a faulty compressor or capacitor, replacement might be necessary. Replacing the entire window unit is often more cost-effective than repairing a faulty compressor. A new window unit can cost between $150 and $500 USD, depending on size and features. Capacitors are a cheaper fix, usually in the $10-$30 range but you must be knowledgeable on how to replace it safely.

Safety Warning

Always unplug the AC unit before performing any maintenance or repairs.
Never work on electrical components when the unit is plugged in.
Be cautious when handling capacitors, as they can store an electrical charge even when unplugged. If unsure, seek professional help.
Avoid working on the unit in wet or damp environments.
If the unit is still under warranty, check with the manufacturer before attempting any repairs, as this could void the warranty.

Tools You May Need

Screwdrivers (Phillips and flathead)
Fin comb (for straightening bent fins)
Soft brush
Multimeter (for testing electrical components – advanced)
Insulated gloves (for electrical safety)

FAQ

Q: Why does my AC unit blow warm air even when it’s turned on?
A: The compressor is likely not running. This could be due to a faulty capacitor, overheating, or other electrical issues.

Q: How do I know if the capacitor is bad?
A: Look for signs of bulging, leaking, or physical damage. Also, if the compressor hums but doesn’t start, the capacitor is a likely culprit.

Q: Is it safe to replace a capacitor myself?
A: Replacing a capacitor involves working with electricity. If you’re not comfortable doing so, it’s best to consult a qualified technician.

Q: How long should I let the unit cool down if I suspect overheating?
A: Allow the unit to cool down for at least 4 hours, or preferably overnight, before plugging it back in.

Conclusion

A window unit AC with a compressor that won’t kick on can be frustrating, but by following these troubleshooting steps, you might be able to identify and fix the problem yourself. Remember to prioritize safety and take your time. If you’re not comfortable with any of the steps or the problem persists, don’t hesitate to call a qualified technician for assistance.