Gas refrigerators use an ammonia and hydrogen solution to create cool temperatures. They do this by -- paradoxically -- heating up the solution. As the solution cycles through the evaporator coils, it evaporates at one point, creating cool temperatures. This system will not work well if the fridge is not properly installed. It may work well enough to cool down the small freezer but not the larger fridge. Norcold N300 refrigerators need to be on a level surface, and they need proper ventilation, especially overhead. A roof vent works well, as does a carefully placed fan. Make sure your fridge is level and has good venting.
The fridge and freezer on a Norcold N300 have separate temperature controls. Check to make sure their settings are correct. If the fridge is too warm, the control may be on the wrong setting. Alternately, the fridge control itself may be broken. In a related issue, the thermostat in the fridge may also be malfunctioning.
The freezer is an isolated unit so it is better able to keep cool. The fridge, on the other hand, is much more exposed. If the door is open and closed often -- or it is left sitting open -- the fridge may feel much warmer than the freezer. Or, if the door gasket is broken or otherwise not sealing properly, this will also cause the fridge to feel warm but the freezer to still feel cold.
It only takes a couple of hours for the freezer to cool down and start running well, but it can take up to three times that long for the fridge to work well, according to the RV Mobile Inc. website. If you've just installed your fridge and it still feels warm, it's possible that it needs some time to become fully functioning.