no heat on 2002 Mercury Sable

Cold air blows out of the vents when I place the knobs on any selection to receive heat(ex defrost/feet or heat to blow out on face/feet) Why I do not get any hot air but the AC works?

Asked by for the 2002 Mercury Sable
You may have a thermostat that is stuck open, or a blend air door in the dashboard that is not functioning properly.
It could be A malfunctoing actuator vaulve controling hot water intering the heater core. The actuator runs of vacum pressure, checking the vacum hoses would be a good place to start diagnoses.
1 more answer , 1 more comment
i had the same problem. My mechanic cleaned out heat pump and changed coolant. works great now
theres no heat pump on a car its a heater coil