Raccoon sleeping on air conditioner

Window-Mounted Room Air Conditioner Troubleshooting

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A room air conditioner is like an entire central cooling system in one small package. It has the same basic components but in smaller form for the reduced duty of cooling a room instead of a home. A typical unit has the following components:

  • Face panel with filter
  • Evaporator coil (the one that gets cold)
  • Fan or blower (blows air through cold evaporator coil into room)
  • Thermostat
  • Compressor
  • Condenser coil (the one that gets hot; looks like a car radiator)
  • Condenser fan (blows air through hot condenser coil to outdoors)

The whole package is neatly housed in a metal enclosure and sits partly in and partly out of your room’s window. Now let’s take a look at some possible problems you may run into and how to fix them.

PROBLEM: Water Drips From Front Panel

Possible Cause:

The moisture condensate from the evaporator coil drains onto a metal pan at the bottom of the unit and runs outdoors through a hole or condensate drain tube in the back. Water dripping from the front of the air conditioner means that the pan is not sloping down toward the exterior but rather into the room.

Possible Solution:

Correct the slope of the unit so that the pan slopes slightly downward toward the exterior. Many units are designed to be installed level, while the pan itself is sloped; the pan is properly sloped when the unit is level.

PROBLEM: Air Conditioner Cycles On and Off Too Frequently

Air Conditioner Cycles On and Off Too Frequently

Possible Cause:

Thermostat or temperature sensor not reading accurately.

Possible Solutions:

  • Confirm that the thermostat sensor is properly positioned near—but not touching—the evaporator coil; carefully adjust the thermostat wire, if necessary.
  • Ensure the thermostat and front panel are not obstructed by drapes or other objects.
  • Check that the condenser coil is not obstructed with leaves and that its fins are not damaged or bent; repair bent fins with a fine comb.
  • Have the unit serviced and checked for a refrigerant leak if performance continues to worsen.

PROBLEM: Air Conditioner Not Cooling

Possible Causes:

Dirty air filter or dirty or damaged condenser coil.

Possible Solutions:

  • Clean the air filter as directed by the manufacturer.
  • Clean and inspect the condenser coil on unit exterior.
  • Check condenser coil for damaged or bent fins; repair bent fins with a fin comb.

PROBLEM: Unit Will Not Turn On

Close up of Air Conditioner Studio Shot

Possible Causes:

A unit is not plugged in completely, or the circuit breaker has tripped or the fuse has blown.

Possible Solutions:

  • Provide well-seated power plug connection; do not use an extension cord, which may not be rated for the high power draw of an air conditioner.
  • Reset the circuit breaker or replace the fuse for the air conditioner circuit.

Warning: A fuse must have the proper amperage rating for the circuit. Do not use a fuse with a higher amperage rating than the circuit wiring. For example, never replace an old 15-amp fuse with a new 20-amp fuse.

PROBLEM: Unit Repeatedly Trips Circuit Breaker or Blows Fuses

Close up of fuse box

Possible Causes:

Inadequately sized circuit (circuit is overloaded). Most window air conditioners are designed to run on a standard 120-volt, 15-amp circuit, although large units may require 240-volt, 20-amp circuits. Ideally, air conditioners should be on dedicated circuits that are not used by other devices. If there are other appliances using the same circuit as the air conditioner, the circuit can be overloaded, tripping the breaker or blowing the fuse.

Possible Solutions:

  • Turn off or disconnect other devices and appliances using the same circuit.
  • Install a new, dedicated circuit for the air conditioner.


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