Have Ford Questions? Ask a Mechanic for Answers ASAP
Your AC system has a vacuum leak. The mode actuator is vacuum controlled and when it looses vacuum, it diverts to defrost to allow proper clearing of the windshield for safety. Check the vacuum lines under the hood near the passenger side of the firewall and make sure it is connected and not broken. If the vacuum line is intact, then you will have to locate the cause of the vacuum leak under the dash starting on the passenger side of the dash behind the glove box where the vacuum line enters the inside of the vehicle and follow it to the control panel for the AC and then to the actuators under the dash.