Why does my 2010 dodge nitro heater does not get hot, it only blows warm air. even after running for over one hour.

If the cooling system is full of liquid, the thermostat may not be closing when the engine is cold.

Most likely the thermostat broke. I expect that you have an older Hyundai and never had the anti-freeze changed. When the engine is cold the thermostat is closed which causes the engine to warm up more quickly. A warm engine runs more efficiently (less gas) and more smoothly. When the engine temp reaches a certain temp the thermostat opens and then allows the hot engine coolant to run through the lines to the heater core. The heater blows air over the heater core which produces the warm air that warms up the cabin. Thermostats used to be cheap and easy to change. I would suggest a web search for how to replace the thermostat. Something like 'hyundai accent 2002 replace thermostat".

Does the car heat up to operating temp. Sounds like a thermostat problem. Could even be the heater control switch. Could be the heater core.

Check for air in the cooling system - tighten carefully all hoses especially ones by expansion tank. If motor on cool down sucks in air instead of water an air bubble could restrict the flow of coolant into the heater core.

Blend air door inop, either from vacuum leak, bad check valve or bad actuator.

could be low on antifreeze, or if antifreeze is too weak it can freeze up and you wont get any warm antifreeze through the heater core, if its blowing sort of warm but not hot it could be thermostat, and maybe even the hot cold switch is not working

where did you buy your thermostat? if you bought a fail-safe style thermostat it could have been no good before you even put it in. also is your tempeture gauge coming up to operating temp?? if it isnt your thermostat may be stuck in the open position allowing the coolant to circulate freely and not actually warm up. i would also check the lines going into the heater core. if one line is hot and the other line is cold than your heater core is probably in need of a flush or replacement.

I would 99% doubt its a clogged core. Have the blend door checked (its a door that cycles between hot and cold)

you can change the thermostat yourself for under 20 dollars. if you dont know how go to an autozone and they will assist you.

could be a pluged heater core back flush heater core. or heater controls aren't functioning properly