Why do I have cold air on my 2008 nitro r/t

May need the thermostat replaced. Make sure the engine is getting to operating temperature. Also check the coolant level.

Thanks, checked my levels, looks a little low, will know in the morning.. Fingers crossed

Not hot air, just warm air with the heat on, cool air when the defrost is on, thermometer is registering half way between cold and hot.. Any ideas?

Sound like it is showing normal. First check to see that both heater hoses are getting hot. If so, then probably a plugged heater core that would need to be back flushed, or the climate control door is not adjusting for cold to hot. Blends in the outside air to mix for proper cabin temperature setting.