Before I parked my car the heater was working when I started the car the heater would not blow hot air

Heater was working fine. Came out from shopping and heater was not blowing hot air. AC works fine. The position selector runs through all positions without a problem. I have check fluid level it was a little low so I topped it off bleed the air out of the system as best I could. I noticed this morning that there was still a little air sputtering but not a lot mainly fluid. Any suggestions on what I need to do