This could be a cooling unit issue or a problem with the thermistor.
IF you have a volt meter you can ohm out the thermistor, click HERE and see page 20. IF you do NOT have a volt meter what you can do is leave the connector you see on page 20 unplugged and try running the fridge, when the connector is disconnected the fridge should default to FULL cooling. IF it gets cold bad thermistor, if it does not get cold then the cooling unit could be the problem. Also make sure you check the door seals, get a dollar bill and place it between the the seals all the way around the box, the bill should not fall at all between the seals.
Cooling unit, a cooling unit can rupture or become blocked, the freezer will always get cold long before the box will so it is very possible to have an issue with the cooling unit. For a rupture you might smell ammonia or see a yellowish powder on the back of the fridge. For a blockage you might not have any symptoms at all but no cooling ON BOTH LP AND AC power. Once a cooling unit becomes blocked it normally needs to be replaced. I have had some owners tell me tapping on the absorber coils with a rubber mallet sometimes works or pulling the fridge flipping it several times and letting it stand level for about 12 hours will help but that only works some of the times. Make sure the fridge is level, if it is not level re-level it and let it sit for several hours and trying running it again.
IF you have more questions or concerns please feel free to contact me, follow ups are included.
IF you are satisfied with my efforts please feel free to select a STAR rating on the page. ROBERT