Window Air Conditioner Troubleshooting (7 Problems & Fixes)

Window air conditioners can be a godsend to deal with the scorching summer heat. Like all appliances, it is also exposed to mechanical and electrical defects as time goes on. Repairs are expensive and time-consuming; you will need to have routine maintenance to prevent the need for a professional air specialist visitation. To protect the longevity and cooling performance of the unit, here is some basic window air conditioner troubleshooting that you can perform without any technical skills.


The Many Components Of Air Conditioners That Might Fail

Before we begin troubleshooting, let’s familiarize ourselves with the critical moving parts of an air conditioner needed for cooling and might malfunction one day.

  • Face panel – The removable plastic or metal cover of the AC unit. It protects the air filtration system from foreign objects. Face panels are typically snapped on through tabs, clips, or screws.
  • Filter – Protects the air conditioner’s components from airborne dust, dirt, lint, hair, and other particulate matters. Depending on the filter type, it is either made of a thin, pleated screen or dense fiberglass fibers (HEPA filter).
  • Refrigerant – A working fluid that circulates in the air conditioning systems. The refrigerant will cycle in liquid and gaseous form between the coils to capture heat and cool the air.
  • Evaporator coil – Cool the air by converting refrigerant from liquid to gas. It is composed of copper tubes with aluminum fins.
  • Condenser coil – Trap and release hot air outside by converting refrigerant from gas to liquid. It is also made of copper tubes with aluminum fins.
  • Compressor motor – Help moves the air throughout the AC unit and compresses the refrigerant agent into a gaseous/ liquid state. It is typically located between the evaporator and condenser coils.
  • Thermostat – Monitor the temperature of the room air to regulate the AC operational cycle. Made of a bimetal strip bolted together that will expand and contract.
  • Compressor fan – Operates at high pressure to volume ratio that blows outside hot air.
  • AC blower – Located on the other end of the fan that moves air over to the evaporator coils for cooling.
  • AC capacitor – Store and transfer energy to the motor that activates the air conditioning cooling system. The capacitor is connected to the compressor and fan motor with two electrical terminals.
  • Reservoir/ Drain pan – A collection tray at the bottom of the unit collects the extracted moisture from the hot air. It prevents excess moisture from leaking out.
  • Drain port/ hole – A small valve that drains and removes the excess moisture outside your home.

Safety Precautions

While it is relatively easy to self-maintain a window AC, there are a few safety precautions you will have to practice to prevent the risk of electrocution.

Unplug the window AC’s power cord from the wall outlet and ensure it is disconnected from any electrical sources.

Let the capacitor discharge before attempting any cleaning or repair. The AC capacitor might still be storing electrical energy even if it is switched off. Use an electrical test pen/ screwdriver to touch the metal parts to confirm if there is any electricity left. If you are not comfortable performing the cleaning, you should leave it to a professional AC technician.

1. Window Air Conditioner Is Not Blowing Cold Air.

The most complaint issue of a window AC, yet it is the easier to solve. An air conditioner that does not cool is caused by:

  • A dirty air filter
  • A dirty evaporator/ condenser
  • Bent fins
  • Low/ leaking refrigerant
  • A faulty compressor
  • A faulty capacitor

The first thing to do is clean the air filter. Pop-out the panel and carefully remove the filter. Gently vacuum away the dust, hair, and dirt, or use a wet rag to remove stubborn dirt. Leave it air-dry completely before reinstalling the filter. We recommend doing the filter cleaning every month or less.

From time to time, the evaporator and condenser coils require cleaning too. A wet rag should do the trick but do not apply force on the coils and fins. Straighten the bent fins with a fin comb.

If the window AC is still not cooling, check the refrigerant line. You will need a qualified AC service professional to perform a refill or repair if it is below the threshold level.

Inspect the compressor or capacitor for any bulge, leakage, or cracks. You can manually check the capacitor condition using a multimeter. Touch the red and black probes’ electrical terminals. If the reading does not match the capacitor’s listed rating, the capacitor is broken and likely is the compressor. Again, a technician is required.

2. Water Is Dripping From The Front Panel.

It is either caused by a clogged drain port or a drain pan that isn’t adequately sloped. When moisture is extracted from the evaporator coil, the water will flow through the drain tube and expel outside the house.

Thankfully, you can repair a dripping window air conditioner on your own. Ensure the drain pan is adequately slopped towards the back for proper drainage. Do so by mounting the window air conditioner level on the window sill and around a lower 1/2 inch slope for the back unit. You can use a bubble/ spirit level to verify. For a clogged drain port, pour water down the drain port to flush out any visible particles. Some vacuuming might be needed to remove any stuck materials.

3. Rattling, Buzzing, Or Humming Noises From The Window AC.

If abnormal noise comes out of the AC during operation, it could be signs of a failing compressor or fan belt. You will need to replace the internal parts before it wears out and break down. We recommend sending the unit back to the manufacturer for repair or hiring a certified air technician.

4. Strong Odors Emit From The Window Air Conditioner.

Depending on the odor type, if it is a distinctive musty smell, mold, mildew, germs, or bacteria could be growing on the compressor or coils. Microorganisms thrive in dark and humid conditions like inside the AC. The root cause is likely that the window AC is dormant for some time, e.g. during the winter season, and is not kept in a dry place. You will need to perform a thorough cleaning to remove every bit of microorganisms inside the window AC before using it. Ensure the room humidity is at an ideal level (30% to 50%) to prevent the recurring issue.

If it is a burning smell with smoke coming out from the window unit, turn it off immediately and air out the smell. There is likely a burned circuit board, capacitor, compressor, or other electronic components causing it. Hire a certified technician for inspection or send it back to the service center for repair. Alternatively, you can also replace it with a brand new unit.

5. Window AC Will Not Turn On.

It is likely that the AC is not getting any power source due to a faulty power cord, bad wall outlet, or trip circuit breaker. There is also the possibility of a blown fuse and malfunctioned electronic parts.

First, examine if the power cord is damaged or frayed. If it is, the power cord should be replaced.

If the power cord is in good condition, try plugging it into multiple wall outlets with local voltage and see if the window AC can be turned on. You can also test each electrical outlet with a non-contact voltage tester or a digital multimeter.

If the window AC is still not responding, it is likely due to a burned fuse or damaged circuit board. The root cause is usually irregular voltage or amperage, and you will need to send it back for repair. Never use a step-up or step-down transformer in a window AC.

6. Window AC Keeps Tripping A Circuit Breaker.

Overheating, electrical, or ground fault could cause the window unit circuit breaker to trip repeatedly. It is usually triggered by a power surge that shorts or overloads the circuit in the wiring. Most window AC is designed to operate on a U.S. standard 120-volt, 15-amp circuit with 500-1,500 watts of electricity. Reset the breaker and always plug the window AC into a dedicated electrical circuit not shared by other appliances, especially those that need constant power like a refrigerator. Do not plug into a non-local power outlet. For self-repair, a blown fuse must be replaced by the same amperage rating fuse i.e. 15-amp for the circuit. Nothing more, nothing less.

7. Window Air Conditioner Cycles On And Off Frequently.

Also known as short cycling, the root cause of the window AC turning on and off are caused by a faulty thermostat, a poorly positioned AC, leaky refrigerant, dirty air filter/ evaporator/ condenser, or a wrong size air conditioner. Here are the solutions:

First, check on the placement of the thermostat. Adjust the position, so it is not obstructed by curtains, sofa, table, or touching the evaporator coil. Next, check if the thermostat sensor is dirty or dusty. If it is, carefully unclip it from the evaporator and wipe it clean.

If the thermostat is working fine, the size of the window AC could be the issue. A small window AC (low BTU ratings) in a large room size could lead to neverending cooling. Conversely, a large window AC (high BTU ratings) used in a small room space could cause short cycling. Measure the room size you intend to place the window AC and get a corresponding unit with matching performance.

A dirty filter, condenser, or evaporator coils can also cause the AC to turn on and off frequently. Clean any dust, hair, debris, or fallen leaves that could lead to blockage. Be extra careful not to damage the filter or bent the fin during cleaning.

Last but not least, a leaky refrigerant can also cause the window air conditioner to turn on and off irregularly. If you suspect that is the case, hire an air technician specialist to perform the checking.


Final Thoughts

Routine checks and maintenance are the keys to a long-lasting window unit. Always give the window AC a deep clean when shifting into a new season or before turning it on for the first time in months. Protect it from external elements by covering or dissembling and storing it in a shelter when not used for an extended time.

With that, you should have a good understanding of how a window air conditioner works, the issue that might arise, and what can be done to fix it. If our window air conditioner troubleshooting cannot resolve the issue you are facing; you will need to hire an air specialist for repair. If there is a need for a brand new unit replacement, check out our best window air conditioners recommendation.

Max Fernandez

A loving father and a dedicated reviewer for airfuji.com with more than 1000 air purifiers under his belt. Max Fernandez is also one of the million patients currently suffering from asthma. Feel free to nudge him if you have any questions.