2000 Taurus, no heat
 

I have a 2000 Taurus that I can't get to throw heat, I have changed the thermostat, checked to make sure that actuator is opening the doors properly under the dash and blew compressed air through the system to check for blockage in the heater core, the temp gauge stays right where is should be. I am about ready to give up on it, any suggestions of what else to try would be greatly appreciated, thank you.