02 dodge ram, 115,000 miles. My heater is only blowing cold. I checked the heater hoses and they are both hot, so i don't think it's the heater core, and I don't have a coolant leak. The radiator, thermostat, and water pump were replaced in september, so they're fine. The blower motor resistor prob needs to be replaced since it only blows air on high, but i don't know if that's related. Something I noticed this year that just dawned on me is I was noticing some dark foamy looking stuff on the floorboard that would accumulate when i ran the a.c. this summer. Could that cause something to not be sealing, perhaps permitting cold air to blow when I run the heat? Thank you in advance.

 

Do you smell antifreeze in the cab?

 

Sorry hit enter too quick!! might have a vaccum leak and its not letting the lines open to the core

 

or blend doors which there seem to be a lot of thread on with others having the same issues