Why does my 24VDC fan draw much less current than labeled?
The electrical motors have (as a rule) high efficiency. That is why the current consumption highly depends on the motor mechanical load. For example, if you try to stop the rotor, the current should increase at least twice. 

When the fan works it is differently loaded, depending on the airflow. On the next picture, you can see, that the efficiency is maximal when the airflow is limited by the pressure difference - i.e. when the fan have to make to work in order to move the air:



So, if you test the fan in idle mode it will consume less power.