Sounds like the mix door, a known problem on fords. It's a rather stupid design if you ask me. If that is your case, a heater core bypass would allow you to have cold blowing AC. However, if your mixing door isn't closed all the way, you still won't be able to achieve the system's maximum cooling output. It is probably cheaper and easier than fixing the mixing door, but I would still recommend fixing it.
Based on my understanding of how this system works, if your mixing door is stuck, in the winter you won't get as much heat either. You are obviously getting air going across the evaporator coil. Let's just say 50%. That's 50% of the air that won't be going across the heater core. However, it is possible your mixing door isn't stuck, but it just can't close all the way. In which case, you will be able to divert all the air across your heater core.
Here is a link to a heater core bypass kit.