Know Two Common Causes Of Moisture Intrusion When Using A Window Air Conditioner And How To Fix Them

Posted on: 14 April 2016


If you notice water running down the wall near your window air conditioner, you will need to investigate and repair the problem before it causes significant damage. There are a couple of common air conditioner-related causes of moisture intrusion into your home; below is a list of these and what you can do to correct the problem once it is discovered:

Unit not level inside window

A window unit functions by removing heat and moisture from the ambient air; this is accomplished by passing warm, humid air over an evaporator coil where the water vapor condenses and drips into a collection pan. Depending on the unit's age and design, the water is either recycled for use in cooling the condenser coil, or it is drained at the rear of the unit to the exterior.

However, if the a unit is not mounted perfectly level, the water may collect at only one end of the collection pan. Water that collects at the front end of the pan may overflow and pour out into the space beneath the pan, ultimately running down the front of your interior wall beneath the air conditioner. This is the primary sign that your unit has not been properly leveled.

If you suspect your window air conditioner isn't level, it is a simple matter to confirm and to correct the problem. Place a framing level across the cabinet of the air conditioner, so it is aligned perpendicular to your home's exterior wall. You will be able to determine immediately whether or not the unit is level. In addition, be sure you don't evaluate the unit's support structure by mistake. The structure may be level or even tilted in an opposite direction, but the collection pan inside the unit itself determines if it will overflow.

Should you discover the collection pan isn't level, you will need to disconnect the air conditioner from its power source and pull the air conditioner out of the window. Next, adjust the support bracket a few degrees downward toward the rear; you can either use a framing level or purchase a built-in window unit level that attaches to the support. Either way, make the adjustment, then place your air conditioner back into position and measure the degree of level using the framing level. If the unit is still not level, remove it again and make further adjustments to the support structure. Repeat the process of removing the unit and making adjustments as often as necessary until you have corrected the problem.

Leaks around the seal or weather stripping

Another source of moisture that may appear as a result of your window air conditioner installation is an exterior leak. This type of leak is caused by poor-fitting weatherstripping or insulating material around the window unit. Rainwater, melting ice and snow and water runoff from nearby locations can be forced through gaps in the weatherstripping and end up on your wall and interior. One clue that a leak may be the source of your problems is that you notice water only after periods of rain or thawing of ice.

Should you believe a leak is the cause of your problems, you can use a few tools to help you locate the source of trouble. First, position a wireless, infrared thermometer to read the temperatures around the unit where it abuts the weatherstripping. A thermometer can reveal areas where warm, exterior air passes through gaps between the insulation and unit. If you discover gaps, you can be confident that water will also pass through these locations.

In addition, you can also shine a flashlight from the exterior side of the unit at the junction between the air conditioner and weather seal. If you can see light through the gaps, then you also know you need to seal the space that will permit water intrusion.

Fortunately, sealing the gap isn't difficult, and it can be accomplished by using a small amount of silicone sealant. Begin by using a general purpose household cleaner and paper towels to clean the weather stripping and unit in the immediate area surrounding the gap. Next, apply a thin line of silicone caulk to the gap, then use your fingertip to rub the caulk into the space. Allow the caulk to dry completely before running the air conditioner again.

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