I have a similiar problem. The AC on my 2003 Altima works fine on the highway, but in slow traffic, or in neutral, the AC stops blowing cold. It seems to cycle to quickly. I've been told it may be the expansion valve, but I don't know where it is or how to check it. I just replaced the pressure transducer which connects to the condenser, because that part was damaged during an impact with debris on the interstate. What is going on?