Your profile notes 1stGen SportTrac V6, but not much else; what year 2001~2005?
What are your AC heat problem symptoms exactly?
If blower only works on high, likely bad blower motor resistor.
Here's a video on replacing that resistor:
If air blows out of some vents, not others, likely bad vane actuator behind glove box.
Could be a clogged HeaterCore, bad\leaking HeaterControlValve, bad\stuck ThermoStat,...
Any recent Coolant system maintenance or changes\mods: ThermoStat, Housing, CoolantFlush+Fill,...?
Do HeaterHoses get hot with heat switched on in the Cab?
Does engine come up to normal operating temp, ~halfway on your ClusterGauge.
Any coolant smell or leaks?