The evaporator of the dehumidifier must become evenly cold. The evaporator is the 1st register after the air filter. Not every dehumidifier allows you to touch the evaporator with your finger, as in this example. Do not carelessly stick your finger into an electrical appliance that is in operation.

If the evaporator is not cold, there is a defect in the refrigerant circuit. 

The fan must also be working for a dehumidifier to be able to dehumidify properly.