Window air conditioner repair: what an owner can check and when to call a technician

Start with the maker's troubleshooting list

Midea's heat-pump window manual includes a troubleshooting list and says to review it before calling for service, because it may save you time and expense. It adds that the list covers common occurrences that are not the result of defective workmanship or materials.

GE Appliances publishes support articles for what it calls room air conditioners. Federal rules use the term room air conditioner, and they include window units in it. This page quotes both makers so you can compare their advice with your own manual.

Federal refrigerant rules in the Code of Federal Regulations (CFR), at 40 CFR 82.152, list window air conditioners as small appliances. The rule defines a small appliance as any appliance that is fully manufactured, charged, and hermetically sealed in a factory with five pounds or less of refrigerant.

If you are still choosing a unit or a window, the guide to window air conditioner types covers that ground.

When the unit will not start

Midea's troubleshooting table lists several causes when the air conditioner does not start. The wall plug may be disconnected. A circuit breaker may have tripped. The plug's current device may have tripped. Or the power may simply be off.

The same Midea table says cooling may not occur until room temperature rises above 60°F. GE says that if the room is already 64 degrees Fahrenheit or below, the thermostat cannot turn on the compressor.

Midea also says the compressor stops when you change modes, and to wait 3 minutes after setting cool mode. On safety, Midea says not to operate a unit with a damaged cord, plug or circuit breaker. It says to discard the unit or return it to an authorized service facility. Another Midea manual says a damaged power cord cannot be repaired and must be replaced with one obtained from the product manufacturer.

For a central system that will not start, see why an AC will not turn on.

Running, but the room stays warm

GE's first checks for a room unit that is not cooling well are about the room, not the machine. It says to make sure the unit is properly sized for the room and not too small. It says curtains, blinds or furniture in front of the unit restrict airflow and affect cooling. It also says to make sure windows are not open, letting warm air back in.

GE says a very hot room takes longer to cool, because heat is stored in walls, furniture, rugs and draperies. Its advice is to turn the unit on before the room heats up whenever possible. Midea's table makes the same point about stored heat in walls, ceiling, floor and furniture.

Settings matter too. GE says the highest setting on a knob dial gives maximum cooling, while a lower setting does so on digital controls. Midea lists louvers aimed poorly as a cause; louvers are the adjustable slats that direct the air. ENERGY STAR says not to put lamps or TVs near the unit's thermostat, because the extra heat makes it run longer.

Midea lists a temperature sensor touching the cold coil as another cause. The Department of Energy says a window unit's thermostat sensor could be knocked out of position.

The Department of Energy says a clogged filter restricts airflow and reduces the unit's ability to cool. Midea also says to check for obstructions blocking the outdoor intake and exhaust, and clear them. For room size, see the window AC size chart.

Ice on the coil

GE says ice on the indoor coils can make the unit stop cooling well. It says ice may even cause the unit to spit water or ice out of the front. GE names three primary causes: the outdoor temperature, the fan speed and a dirty filter.

On temperature, GE says a cool evening below 70 degrees Fahrenheit is one cause of ice on a window unit's coils. Another GE article says running a room unit when it is 70 degrees or below outside limits its cooling. A third says frost from cold outdoor air will not usually harm the unit but does waste energy.

On fan speed, GE says a low fan with the thermostat at a higher setting leaves too little air moving over the coils. That moisture then freezes, in GE's words. On the filter, GE says a dirty or clogged filter may also cause icing. Midea adds that trapped particles in the filter can build up frost on the cooling coils.

To defrost, GE says the quickest way is to turn the unit off and let the room air melt the ice. Afterward it says to set the temperature to the middle or a warmer setting and the fan to its high cooling speed. Midea's manual says to defrost by setting the unit to FAN ONLY mode.

The guide to an AC freezing up covers the central-system version.

Water: normal outside, not normal inside

GE explains where the water comes from. Moist room air passes over the cold indoor coil, and water condenses on it. The water collects in the base pan and flows to the rear. GE says it is normal to see water dripping on the outdoor side.

GE says room air conditioners have a slinger ring around the rear fan blade. The ring picks up water from the base pan and throws it against the condenser coils. GE says spitting, spraying or dripping on the outdoor side is normal. Midea says heavy dripping outside is normal during excessively humid days.

Water inside the room is different; GE says that is not normal. GE says the unit may be tilted slightly into the room. It should be level or tilted slightly to the outside, about 1/4 inch, so excess water drips outside. GE adds that a dirty air filter can cause moisture to drip on the floor inside.

Midea says not to drink water drained from the air conditioner, because it contains contaminants.

Midea recalled about 1.7 million U and U+ window units, in a recall announced by the Consumer Product Safety Commission (CPSC) on June 5, 2025. The CPSC notice says pooled water in them can fail to drain quickly enough, which can lead to mold growth. It says owners should immediately contact Midea for a repair. Midea's manual says to stop operation and close the window in a storm or hurricane. Midea says operation with windows opened 'may cause wetting of indoor and soaking of household furniture.' For water from a central system, see an AC leaking water.

Filter and cleaning

GE says to clean a room unit's filter every 30 days, and Midea says to check it at least once every two weeks. GE says you may vacuum it gently with a brush attachment or wash it in warm water. Midea says never to use water hotter than 104°F. GE says not to put the filter in a dishwasher, not to reinstall it damp, and not to run the unit without it.

Midea says to unplug the unit before cleaning to prevent shock or fire hazards. It also says not to clean the air conditioner itself with water, because water may enter the unit and cause an electric shock. GE says clogged outdoor coils may be professionally cleaned. It does not recommend a garden hose or pressure washer, since you are more likely to get water into electronic areas.

Noises, warning signs and who to call

Some sounds are normal. Midea says airflow sound is normal, and a 'da-da' sound for thirty seconds at start-up comes from the compressor starting. It lists window vibration as poor installation and says to check with the installer. For a unit that turns on and off rapidly, Midea lists a dirty filter first, and GE says the unit may be oversized.

The Department of Energy says compressor and fan controls could be worn out from having your system turn off and on too frequently. It says to contact a professional to check your unit's electrical connections. Midea says to disconnect the power if strange sounds, smell or smoke come from the unit. It also says never to use the unit if it is not working properly, or if it has been dropped or damaged.

The Environmental Protection Agency (EPA) says technicians who maintain, service, repair, or dispose of equipment that could release refrigerants into the atmosphere must be certified. It says apprentices are exempt if a certified technician closely and continually supervises them. It says a technician is an individual who performs activities that include 'adding refrigerant to or removing refrigerant from an appliance.' It lists Type I certification as 'for servicing small appliances.' Midea's heat-pump manual warns that the refrigerant it uses, a type called R32, is flammable and may not have an odour.

If the unit is under warranty, Midea says warranty service must come from Midea Consumer Services or an authorized Midea servicer. The Department of Energy lists a life span of 10 to 15 years for room units. For deciding whether to repair or replace an older unit, see repair or replace.