I am running a Frigidaire model LAD704TDL dehumidifier in my basement. It is not adequately dehumidifying the air.

Let me start with a little background info: The basement (28' x 46') consists of three rooms, with a concrete slab and poured concrete walls. The basement is dry (double drain lines along outside perimeter as well as interior drains under the slab, Bituthene waterproofing on the exterior walls and UGL DryLok on the interior walls. The moisture problems come from living in NC and with woods all around the house, so we have very high relative humidity for most of the summer. We are not running any A/C in the house, so the the temperature in the basement gradually rises to about 80 by mid July. We've been here for 3 years.

When we first moved in, we had a mold/mildew problem in the basement. We bought a Frigidaire dehumidifier from Lowes (the predecessor to the model listed above). Both models are rated to remove 70 pints of water per day. The first one worked great. At first we had to empty the bucket 3-4 times a day and it effectively dried the air. It lasted for 2 years until the unit started forming ice on the coils to the extent that we couldn't use it. We got it replaced under warranty.

The dehumidifier we have now has run for a little more than a year. It is located in the smallest of the three rooms (12' x 28') with an open doorway. This unit is set at 60% and runs continuously, rarely lowering the humidity below 70%. It takes almost a week for the bucket to get full. The unit is clean; the filter is checked and cleaned as recommended and is only a little dusty when checked. Consequently, I've had some issues with mildew/mold growing on some particle board shelves and some leather goods in the room.

I would appreciate any information or ideas as to what could be the cause of the problem and/or suggestions to remedy this issue.