Why isn't outdoor temperature displayed on indoor unit?

Double check the batteries to make sure they are installed correctly. If one of the batteries in the outdoor sending unit is in backwards, it will not send the outdoor data. On the indoor unit, there is typically one battery that is used for receiving the signal from the outdoor unit. If all of the batteries are in correctly but that one, you will see the display and the indoor temperature information, but the outdoor information will not be displayed.