Window Mounted Air Conditioners

The summer months bring heat waves and humidity.  Unfortunately, you don’t have central air due to your current living accommodations.  A quick, inexpensive fix might be to mount an air conditioning unit in your bedroom window.

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

window ac
  • Face panel with filter
  • Evaporator coil (the one that gets cold)
  • Fan or blower (blows air through cold evaporator coil into the 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. Even with yearly maintenance, there are some common issues that can occur with window units. Here’s a look at how to fix them.

Water drips from the front panel

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.


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.

Water drips from the unit on the outside

In older buildings, damage to the exterior of a building can be caused by the air conditioner drip. Wherever a window mounted air conditioner is installed on a 1950’s or earlier low quality brick building, mortar deterioration can occur. If there are holes in the mortar, the constant drip can cause damage in the interior wall.


In most air conditioning units, there is a place to insert a small drainage hose in the base plates. Find the knock-out plug that you can punch out and put the drain hose in. Divert the drip from your unit to a better place, but of course, be respectful of where the drip will be going.

Make sure it doesn’t become a water torture device on your neighbour below, or to passersby on the sidewalk!

Air Conditioner Cycles On and Off Too Frequently

This could be caused by the thermostat or temperature sensor not reading accurately.


  • 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 fin comb.
  • Have the unit serviced and checked for a refrigerant leak if performance continues to worsen.

Air Conditioner Not Cooling

A dirty air filter or dirty or damaged condenser coil could cause the unit not to cool any longer.


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

Unit Will Not Turn On

This could happen simply because the unit is not plugged in completely, or the household electrical circuit’s breaker has tripped or the fuse has blown.


  • Provide a 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.

Unit Repeatedly Trips Circuit Breaker or Blows Fuses

This could be caused by an inadequately sized circuit (the 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 served by 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.


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