Whirlpool dehumidifier ad35dssi runs, but doesn't collect any water, even in a wet area. Have cleaned filters, no luck.

Glad to hear that you thought to clean the filter, as that would have been one of my suggestions. Because, it's the most overlooked.

But, there is another one that equally overlooked and is probably the number cause of your humidifiers problem. The humidity extraction level is set to HIGH. Lower it to 32 - 35%. If your unit does not have an LED Screen readout, set the control on MINIMAL.

This is what gets confusing about the use of dehumidifiers. They work backwards from what most people think. The lower the setting, the more moisture/humidity is extracted from the house. The higher the setting/numbers, the more humidity remains in the house. The higher setting would be used only in the Winter, because removing all the moisture and humidity will make the house uncomfortable.

If this wet area, you mentioned is a basement. The ambient air temperature at floor level is colder than at chest level and dehumidifiers don't work well in temperatures between 40 & 60 degrees F.
If this is the case, placing the unit up off the floor on a sturdy table, counter, etc that can hold the weight of the unit, plus a full bucket of water will generally solve the problem.

Also, be sure that you're maintaining at least 12" of clear air space on all sides of the unit. If the air flow is obstructed, the unit will run all day and not extract any water.

Hope this helped you troubleshoot and solve the problem. Please let me know. Thanks.