Cooles but will not heat

heat strip is possibly burnt out and will need to be replaced. The strip sits inside the unit right behind the evaporator coil, To access the heat strip you will need to remove the unit from its casing and place it on a level surface.. The heat strip is possibly in a metal casing and the heat strips look like the heat strips in a toaster. The assembly comes out by removal of a few phillips head screws and has an electrical disconnect plug that powers the coil. Take the coil assembly along with the model and serial number to the nearest appliance parts house for replacement part. Good Luck hope this helped you somewhat

Dave