heater problem on 1999 Ford Taurus

I have a 1999 taurus, I have no heat. It will get warm when idoling on the vent setting, but when driving have no heat at all. Think maybe heater core but not sure.

1 answer
A quick method to tell if you have coolant flow through the heater core is to feel and compare the temperature of the inlet and outlet heater hoses. A clogged heater core will have only the inlet hot or warm. A stuck open thermostat could also create this concern.