Ford Focus A/C and over heating?

I have a question concerning a 2007 ford focus with a 2.0 DHOC engine.
When the car is first started in the morning the AC works great, it will freeze you out. After driving for 2 or 3 hours and the car is stopped for fuel or a break, the A/C stops working.
It may blow cool, but not cold. If the A/C is ran the car will start to over heat. None of this occurs until the car is shut off for the first time after driving for several hours.
If the A/c is not ran then the car s tempature will run at normal all day long.
I havechecked freon levals and it says it is good, and I know the A/C compressor is kicking in and running.
What might be some other causes for this issue?

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