Troubleshooting Window-type Air Conditioners Guide & Repair Tips

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Window ACImage by LillyCantabile from Pixabay

Window air conditioners are lifesavers during long hot summers, providing a constant stream of fresh cold air, and a disaster when they stop working. It’s usually on the hottest day of the year.

Let’s have a look at how window air conditioners work and a list of 12 common issues with troubleshooting tips and how to fix them, if possible, before you call an HVAC professional to save you. This also applies to window-type heat pumps.

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What is a window air conditioner?

A window air conditioner is essentially the same as any larger AC unit, but all neatly packed into a small box that is fitted into a window opening with half inside and half outside. Due to its small size, it is mostly used for room air conditioning.

On the room side, you will see a cover with a grill to let the cooled air into your home and behind or inside that grill is a removable filter to catch debris in the airflow and make the incoming air cleaner. To ensure the highest performance and long life, filters should be regularly cleaned. And it is simple to do that: you just have to disconnect the unit from the power supply and then remove the front cover and a filter.

Some AC units may have replaceable filters; others use a fine mesh that is cleaned by washing in soapy water, then rinsed and dried before replacing it.

You should clean the internal filter every two or three months unless you live in a dusty environment or have pets, then once a month would be best. It’s a fast and straightforward way to keep your unit running correctly and your air clean.

How to clean the inside of your AC

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With the window AC’s cover off, you will see the evaporator coil, which has delicate fins on it to help concentrate the airflow through the unit. These fins do get clogged up over time and need to be cleaned. Behind the coil is a fan that blows air across it and into the room.

To see the back of the window AC unit, it needs to be removed and taken outside for proper cleaning unless you live on the ground level and have easy access. Once dismantled and opened up, you will see the small compressor unit sitting between the evaporator coil and the condenser coil, which has its own fan to push hot air back out into the atmosphere.

With the unit opened up, it makes it easy to maintain using an inexpensive cleaner available from your local HVAC shop. Simply spray the coils thoroughly and leave to soak in as recommended, then lightly wash the dirt off with clean water.

Check the coil fins

As the fins on the coils are easily damaged, it’s not advisable to scrub them with anything rough or hard. Use only a gentle water spray to remove the debris. If any of the fins are bent or damaged, you can straighten them using a fin comb, which will improve airflow through the unit.

Dry the unit thoroughly before re-installation, and an extra pair of hands is useful for this part of the operation, in case of accidents.

If you maintain your window air conditioner like this once a year, it will deliver outstanding results, but if you leave it, the unit will eventually give you problems and fail you at the least convenient time.

Summer wake up

If your window air conditioner has been off all winter, then it’s essential to check it over properly before running it for the spring and summer.

Remove it from the window, or, if it’s been in storage, open it up and check it for nests, insects, or small mammals, which may have taken up residence during the winter months. Clear it out carefully with a vacuum and gently wash the coils to remove any debris. If any of the fins are damaged, you can fix them using a fin comb by setting it to the layout of the fins per inch in the coil.

Clean the filter and check the fan blades for any damage. Straighten them out gently to ensure vibration-free running.

Once the unit is cleaned and dry, re-install it and run it up to check that it’s in good condition. Check for leaks of any kind, they could be an indication of something more severe, and if caught quickly, can be repaired easily. If you let it go, it will become expensive and may not be repairable at all.

Freezing up – causes

Another common issue with window AC is freezing up, which can be caused by blocked, dirty coils. Freezing causes overheating, which will lessen the efficiency of the unit. It could also be that the unit has a leak that needs repairing, and the refrigerant topped up.

If you choose a low fan setting along with a low-temperature setting on your window AC, it will most likely freeze up. The AC requires a good airflow to work efficiently, so it’s best to run it on a higher fan setting. The only time you should lower the fan speed is to help lower room humidity when it’s excessive.

The ideal temperature setting should be about 68 F, lower than that will cause the unit to freeze up.

To avoid the problems on the compressor such as overheating, use the garden hose to wash it.

Troubleshooting guide –12 most common problems

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This troubleshooting guide covers twelve of the most common problems with window air conditioners. As is often the case, the most frequent issues are due to a lack of straightforward maintenance. A small amount of care and attention will avoid most of these issues, and your unit will work tirelessly for you day in and day out. Ignore it, and it will get you back.

Problem# 1: The AC doesn’t run.

Possible causes: No electrical power, unit switched off or unplugged. 

Solution: Switch on - Check plug/cable/breaker. Do not use an extension cord.

Problem# 2: Tripped breaker or reset button.

Possible causes: Power surge, overloaded supply, fault in the unit.

Solution: Reset breaker (or change the fuse with the correct rating) and the reset button on the unit. Check power supply is sufficient for the load. If in doubt, call an electrician.

Problem# 3: Frequent breaker tripping.

Possible causes: Overloaded supply or fault in the AC unit.

Solution: Call an electrician or an HVAC technician. 

Problem# 4: The fan produces a low volume of warm air.

Possible causes: Check the thermostat setting.

Solution: Reset thermostat lower to see if the unit starts cooling.

Problem# 5: Fan works but no cooling.

Possible causes: Dirty filters and coils causing low airflow.

Solution: Clean filters and coils regularly to remove dirt.

Problem# 6: The unit turns on and off repeatedly.

Possible causes: Dirty filters and coils causing low airflow.

Solution: Clean filters and coils regularly to remove dirt.

Problem# 7: Fan vibrating.

Possible causes: Fan clogged, blocked by debris, or a faulty motor. 

Solution: Check and clean the fan, Fix damaged blades. If faulty call HVAC technician.

Problem# 8: Fan not operating.

Possible causes: Check switch settings.

Solution: If the setting is correct, the switch could be faulty. 

Problem# 9: Damaged fins on coils.

Possible causes: Fins are easily damaged and will restrict airflow if bent.

Solution: Avoid heavy handling when cleaning and gently straighten fins with a fin comb.

Problem# 10: Coolant leaks.

Possible causes: Damage to coils.

Solution: Call an HVAC technician.

Problem# 11: The compressor is not running.

Possible causes: Check for loose connections.

Solution: Call HVAC technician.

Problem# 12: Condensate leaks inside the house.

Possible causes: The unit may be sitting at a slight inward angle where condensate is missing the drain tray.

Solution: Adjust the angle of the unit, so condensate drips into the tray correctly.

NOTE: Always disconnect the unit from the power supply before removing the covers for maintenance or fault troubleshooting.

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It’s basic stuff

It is an excellent plan to clean your filters and coils a couple of times each year, to ensure good airflow through your unit because air conditioning needs an unbroken, free flow of air to work efficiently. Cleaning the filters is done quickly, and removing debris and dirt from the coils will bring your unit back up to new condition.

It only takes a short time and will guarantee your unit runs efficiently and cost-effectively all year. Just think about how often you clean your car. It doesn’t need to be clean to run efficiently, but you still do it, so why not your air conditioner?

Be aware of leakages of any kind; they could indicate something more severe and, if caught quickly, could be repaired easily. If you let it go, it will become expensive and may not be repairable at all.


As always, it’s down to you, you have the choice, and if you spend a little bit of time on the maintenance of your window AC unit, it will pay dividends, guaranteed. It doesn’t take much time to do, and it is so worthwhile, plus it saves you money in the longer term.

Window AC units are designed and manufactured to the same high-quality standards of full-sized systems and will last for years if you do your bit to keep them clean.

Then you can sit back and relax in a fresh stream of cold air on the hottest of days, knowing you did the right thing, plus you avoided a bill for a technician, this time at least.