Why does my ac only blow cold air, when I'm constantly moving?

What is your question?

My 2015 Nissan Altima starts off with hot air until I am constantly moving. Once I stop at a red light or stuck in traffic, it blows out hot air. I tried to add the refrigerant, but not even that will go into the low pressure valve. I know I have Freon because my car gets cold ac blowing and my compressor is running normal. What else could it be? The fan is blowing fine at any 'level' I turn it to without issues. Help! I don't see any leaks under the car, but then again I'm not sure where else to look.

What makes this problem better or worse?

It’s better when I’m constantly moving

How long has your 2015 Nissan Altima had this problem?

Few days