Diagnosis
Yeah, this one's common. If the fan is running but it's not dehumidifying, the compressor isn't kicking on. The most likely culprit is the evaporator coil being frozen solid, which happens if the air filter is clogged or the ambient temp is too low.
How to Fix It
First, check the washable foam air filter behind the front grille. If it's dirty, wash it with warm water and let it dry COMPLETELY before putting it back. Then, turn the unit OFF at the control panel and unplug it. Let it sit for 24 hours to fully thaw out any ice on the coils inside. Plug it back in and set it to a higher humidity setpoint (like 65%) to see if it starts collecting water.
If That Didn't Work
The refrigerant might be low (a leak) or the compressor start capacitor could be weak. Listen very carefully when you first turn it on—you might hear a faint click (the relay trying) but no low hum from the compressor. That's often the capacitor. It's a silver cylinder usually located in the electrical compartment.
Heads Up
These units are designed to work down to about 50°F. If your crawl space is regularly colder than that, it will ice up and not work. You might need a different model or a space heater to keep the area above that threshold.