I have an A/C/Heater question 2002 KIA Spectra?

My a/c and heater worked fine, then I turned the heater off and turned a/c on, a/c engaged, but blows hot air..constantly! I have freon and it's charged. Was told about a 'door' on the housing of my heater core, that may be stuck open, but I haven't found it. My Haynes book does not reference this problem. I can get to the housing, but can't find a 'door'. Any ideas??

I have an A/C/Heater question 2002 KIA Spectra?
the door happens to be inside of the housing ,but the actuator for it should be on the outside of the housing ,you,ll have to go in under the dash to get to it,and have the car running and switch it from heat to cold to see of it opens,if not that could be the problem, usually its the inside control unit that goes bad,that's the whole control unit where you switch from hot to cold or change it from lower to higher vents,those usually go bad,good luck with it.
Reply:The door is inside the housing,which seperate the heater core from the evaporator core.The blend door is not functioning correctly.Could be trash in the proximity hampering the blend door.
Reply:The "blend door" is in between the heater core and the A/C evaporator. You can't see it or get to it in any way shape or form without removing the entire plenum. Look for a cable or vacuum hose attached to the system. If broken or disconnected, this could be your problem. Some HVAC (heating ventilation air condition) systems have an electric motor that adjusts the blend door. This is harder to diagnose as the pivots could have broken stopping it from moving.
Reply:if the blend door is working you can double check to see if the ac is getting cold by finding the line that runs form the evaporator core and compressor it should get cold