Over the last month or so, with all of this rain, we noticed a bit of mold starting in our basement. We've always had our dehumidifier running so I didn't think to check it at first, but it turns out that our dehumidifer was running but not working. The compressor was kicking on but it wasn't actually pulling moisture out of the air. After buying a new one, I realized that the new one actually got cold, too. So to do a quick check on your own dehumidifier, you can put your hand in front of the grill and see if you can feel cool/cold coming off it. (Dehumidifiers are built like air conditioners and refrigerators - they use a compressor and freon gas.) A better test would be to actually confirm that water is actually accumulating in the tank or coming out of the hose!
And, if you hook your dehumidifier into some sort of plumbing, you don't have to empty the tank on a regular basis.