A dehumidifier works in a very similar manner to an air conditioner. The unit draws air across a set of refrigerated coils called a condenser. Moisture in the warm air collects on the cooled coils and drips down into the collection tray.
The best way to verify operation is to compare the temperature at the condenser to the exhaust temperature. In order to attract moisture the condenser should be at least 20 degrees colder than the exhaust temperature.
Haier dehumidifiers offer a humidistat function which will monitor the humidity in the room, once the humidity rises above the adjusted value the unit turns on, when the humidity level drops below the preset value the unit shuts off.