heater stop blowing hot air only blows cool air

Most likely your heater core is not getting hot water (coolant) in to it. I don't know the particulars on your system but start by checking the radiator itself, cold, don't pop a hot cap..then there is probably a valve to the heater core controlling the flow to the core. Find that, it may be plugged or stuck shut, or the linkage to it. Try opening it by hand, or the core may need to be flushed, especially if at any time somebody put some kind of 'stop leak' in the radiator.

I had the same problem with my heater. Coolant was low, added coolant, now its hot as all heck!!!

Thank you Peter I went all week without heat in my Pacifica , so when i read your answer about putting coolant it worked, so once again thank you.