A- During the hot summer season the interior of air handler is a perfect environment for mold growth. Mold needs water, food and air to propagate. During the hot season the evaporator coil collects moisture from the air in our homes to make us feel more comfortable. Normal dust particles which bypass the filter collect on the interior components of the air handler. Mold spores floating in the air, pass through the air handler via the return, thus, collecting in the condensation droplets allowing the mold spores to reproduce. In a few hot seasons, your air handler can be fully infested with mold growth.