might be a stuck vent door in the dash all vents are working properly
heater core may be partly plugged .
Plugged heater core. Try flushing it.
Assuming you're referring to the heater core, see "Related Questions" below for tons of detailed information about Taurus/Sable heating systems...
How do you replace a heater core in a 1998 Ford Expedition?"
How do you replace a heater core in a 1998 ford expedition?"
no
2 things to look for with heater cores:Plugging up - poor cooling system maintenance can lead to the core plugging.Leaks - pretty self-evident with visible puddles and/or the smell of anti-freeze in the cabin / coming from heater vents.See "Related Questions" below for a good round-up of questions dealing with Taurus / Sable heating & cooling.
A leaky heater core can do that. Also if the AC is not operative, the defrost mode can't dry the cabin air.
Like most water-based exchangers, known as the heater core, a hot liquid passes through the inside of a housing which is covered in metal 'fins'. Air then is blown over this housing where it picks up some of the heat from the heater core and moved through the ducts to the vehicle cabin. See "Related Questions" below for much more about Taurus / Sable heater cores
heater core
Remove the kick plate on the passenger side of the passenger cabin. Remove the heater core water supply hoses. Remove the heater core retaining bolts.
Remove the water from your 1998 Chevy Camaro cooling system. Remove the water supply hoses from the heater core. Remove the heater core retaining bolts. Reverse the process to install the new heater core.