Q: My A/C System isn't working properly. on 1998 Ford Expedition

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My A/C system starts out blowing cold air and after awhile it sounds like a suction vent closes and it starts blowing hot air. It only does it on the front system and not the rear system and I already changed the air vent actuator.What do you guys think is the problem?
(1) Answer
This could be due to icing of the evaporator. There might also be a blend door issue if it's blowing hot air, and not ambient air. If the evaporator is getting too cold then it will freeze the water running through it and stop blowing cold air until the ice melts. You can also check to see if the blend door has moved by looking at the blend door linkage when cold and rechecking after it starts to blow warm.