2001 Infiniti QX A/C

Have to drive several miles before blowing cold air. Clutch is engaged. Low pressure line is hot until it starts cooling. Line instantly turns cold. All pressures look good. Had it checked
at a shop and was told it was compressor but I don't think so because it works so well. Also after it starts to cool it will work the rest of the day. I understand what this is a variable displacement compressor and have used a lot of had pumps like this and they are good or bad most of the time. I think it is the valve on the evaporator coil, but don't want to take it out with out knowing more.