I have a 2003 ram 1500. My heater was blowing very cool air. I replaced my thermostat now the passenger vents blow very warm air and the driver side vents are still blowing cool air. Any suggestions?

 

Common symptom of a clogged heater core, though it could also be a blend door issue also if you have dual climate controls.

 

More likely the blend door. Common failure, especially on a twelve-year-old truck. Mine acts up now and again, but hasn't failed yet (knock on wood).

 

See if both the heater hoses are hot. the in and the out of the heater core. if one is still fairly cool then it could be plugged up. if they are both hot to the touch then it could be the vents as earlier stated. good luck.