No Pressure building up

I have a Kobalt 5hp 80gal single phase unit. I just replaced the pump so I am thinking the pump is not the issue but now I can get no pressure. It runs but builds no pressure. Disconnecting the line going into the tank and supplying air from another compressor the pressure gauges indicate pressure going in. If I take the line off going directly into the tank and push down, there is a release of air but not much.