My dodge nitro originally would blow heat and air on high and nothing on the other settings. This summer the air went out and now the heat seems to have gone out? What are your thoughts?

Low coolant level, clogged heater core. If only blows on high, odds are the blower motor resistor is bad.

I bought a 2008 Dodge Nitro and when I left the lot the heat did not work! Long story short I watched YouTube and read a lot. I flushed the heater core and reversed the hoses and now my heat is running like champ!!! To do it right you have to flush for a good hour!