Don't Let Your A/C's Air Filter Get All Washed Up

Most experts recommend that you change your central air conditioning system's air filter at least every three months. Now imagine doing just that, only to discover your air filter is sopping wet. It's a fairly uncommon problem that can have plenty of consequences for your entire A/C system, let alone your home's indoor air quality.

The following explains how your air filter could end up all wet. You'll also learn how you can stop this problem in its tracks and prevent it from happening in the future.

How It Happens

Believe it or not, water is a significant byproduct of the air-conditioning process. As your A/C system's evaporator coil absorbs latent heat from the air flowing through it, it also triggers a change in the air's relative humidity. The colder air gets, the less able it is to hold vast amounts of moisture in vapor form. As temperatures drop, moisture is forced to condense into liquid form. The resulting condensation falls into the catch pan below the evaporator, where it eventually drains away from the A/C unit and into your home's drainage system.

A wet air filter usually goes hand-in-hand with condensation drainage issues, which can be caused by a number of problems:

  • The drain line for the catch pan could end up clogged with algae and debris, especially if the pan itself isn't being cleaned regularly. Once the drain line is stopped up, water backs up and eventually floods the catch pan. The resulting cascade of water could easily find its way into the intake air duct and the air filter within.
  • The catch pan itself could be damaged in some way. Plastic pans can deteriorate with age or wind up damaged by accident, while metal pans rust and corrode. The end result is a pinhole leak or two that allows water to travel out of the pan and towards the air filter.
  • In some cases, an air filter that's clogged with dust can cause the evaporator coil to ice over. As the ice melts, some of the water can make its way towards the air filter.

What You'll Notice

If there's a leak in progress, you may notice the lower portions of your air filter appear soaking wet. How much water your air filter absorbs depends on the material it's made from (pleated paper air filters are more prone to water absorption than fiberglass).

Even if you haven't checked your air filter lately, it may exhibit many of the same symptoms as a completely clogged air filter in the event it gets waterlogged. This means that your central A/C system will have a noticeably harder time drawing indoor air into the unit. This also places tremendous stress on the blower fan and other components within the unit.

Effective Solutions

The first thing you should do is toss your old air filter and get rid of the water in the intake air vent. You can use absorbent cloth and/or a wet/dry shop vacuum to tackle this important task. You'll also want to vacuum up any standing water around the central A/C unit itself.

Next, get rid of the water in the condensate catch pan and examine the pan itself. The catch pan is located with the A/C plenum, underneath the evaporator coil. Most plenums feature an access door that can be opened with a screwdriver to access the pan and coil.

Carefully inspect the catch pan for any cracks or holes that could cause leaks. Small cracks and pinholes can be fixed with a careful application of epoxy on the affected area. However, larger cracks or holes caused by severe rust and corrosion may necessitate a complete replacement of the catch pan.

If the catch pan isn't the culprit, or if you're still having problems, you should check the condensate drain line for clogs. At this point, you can:

  • Suck the line clear using your shop vacuum
  • Blow the line clear using a hand pump attached to the drain line outlet
  • Use a length of stiff wire or a drain-clearing brush to bust the clog loose

After the clog's gone, it's a good idea to disinfect the drain with bleach or white vinegar. Doing so will prevent algae and mold from taking hold of your drain line as well as other parts of your A/C system. Don't forget to add a fresh, new air filter after you're done. For more information, contact a local HVAC company or visit