1998 Chrysler Concorde AC blows warm air

Start with the easier symptom. The mode doors in the heater box are operated by engine vacuum and are spring-loaded to default to the defrost position when there's a problem with that vacuum supply. That's done for safety. Your feet might freeze, but the windshield will be clear.

Start by looking under the hood at the vacuum hose routing diagram on the sticker. It will show a small plastic hose going to the firewall. Near the firewall is a check valve about the size of a stack of three nickels. Check that hose for breaks and to be sure it isn't disconnected.