2001 dodge ram when you trun the heat on it blowes cool air

1st check your coolant level, if it's low, it won't circulate thru the heater core, and u will have little or no heat (easy fix!). If that isn't the problem, what does your engine temp gauge indicate? Is it running @ normal or low? How long does it take for the engine to reach operating temp? Let me know, as it could be a thermostat problem. If it's stuck open, the engine won't reach operating temp, and u won't have heat. There are a couple of other possibilities, let me know what u find with this info, these are the 2 easiest and common problems.