- 1). Turn off the power to the air handler. Locate the main circuit breaker for the property and set the switch for the breaker that controls the air handler to the "Off" position. Some air handlers may have a separate cut-off switch installed near the unit that can be cut instead of the main circuit breaker.
- 2). Locate the drain line for the unit. These are connected to the drain pan that sits underneath the evaporator part of the air handler. The evaporators are, in turn, hooked up to the ventilation system, so look for them where the ventilation system is installed in the property, commonly in the basement or attic.
- 3). Find the inlet for the drain line in the drain pan. If the line is backed up, the pan may be filled with water. You can either drain the pan out with a container, mop up the contents with a towel and sponge, or feel around on the inside edge of the drain pan for the inlet.
- 4). Take a narrow piece of plastic tubing and insert it into the drain pipe. Continue feeding the pipe into the drain line until you can feel any blockages inside. Move the pipe back and forth against the blockage until you feel the line clear.
- 5). Rinse out the drain pan and drain line with fresh, cold water.
- 6). Mix 1 cup of bleach with 1 pint of warm water. Run this mixture through the drain line to help kill off any mold or mildew inside.
- 7). Restore power to the air handler unit.
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