I have a 99 durango and my heat has decided to not work properly. If it's above 40-45 degrees it comes out warm, any colder than that i got mildy warm air unless I turn it to my windshield vent and it comes out decently warm but no where enough to warm the vehicle up. I just changed the thermostat and topped off my antifreeze and it didn't change anything. You guys have any help? It's supposed to be in the single digits next week so i need to get it fixed. Thanks!

 

i would look at a partly clogged heater core. Try flushing it out and see if that help.. here is a video on some ways to do it ~~>

 

Agreed. I did mine literally about 20 minutes ago, and it blows much warmer now

 

Also check the AUX coolant valve on the right side frame rail too.

 

Whats the deal with this? What does it do?

 

The correct name is a auxiliary coolant pump. Mopar number 55056055AA. The pump helps with coolant flow to the heater core.