1995 Lincoln Town Car Control switch for ac

Most likely you have vacuum-operated mode motors and the vacuum hose is broken or disconnected. The systems are spring-loaded to go to defrost mode for safety when there's a failure. Your feet might freeze but the windshield will be clear. Look at the vacuum hose diagram under the hood. It will show that hose. It will be small, possibly made of hard plastic, and there's some type of check valve in it too. Often on Fords that hose originates on a large multiple vacuum "tree" on the firewall.