why is my heat blowing out warm air on passenger side but cold air on driver side?? HELP

oh its a 2007 dodge nitro...

Your heater core is plugged off, if you go under the hood and reverse the hoses it should clear up for awhile, but you need a new core.

I have been trying to troubleshoot the "lack of heat" for a couple of months. The symptoms were lack of hot air particularly on the drivers side. Checked the anti freeze level, the actuators for the blend door etc , and flushed the heater core a couple of times. Heater core flushed easily with no sign of it being dirty. Dealer diagnosed it in no time. They said heater core and $1400 dollars later the heat works great. They explained that the heater core can and will plug in stages. So even thought you flush it, the tubes at the bottom can remain plugged. The lines are hot and circulating antifreeze through whatever tubes are not plugged. More and more get plugged and less surface of the heater core to make heat. I never realized this could happen to the heater core, always thought they would fail with a leak or plug up completely. Hope this helps. Roger

When you flush it out use air. Water flushing wont remove it. http://www.cargurus.com/Cars/Discussion-c21295_ds536107? actionMessages=Your+answer+has+been+posted.