1998 Mitsubishi Diamante AC not cold

Air Conditioning problem
1998 Mitsubishi Diamante 6 cyl Front Wheel Drive 105000 miles

I have a 1998 Mitsubishi Diamante AC problem. I have replaced the compressor, dryer and expansion tube. Before the new parts were installed, the system was flushed. When recharged, the air blows cool but not cold. The low side will only go down to Approx 70psi, the high side is Approx 150psi. When I bring the RPMs up to approx 2000 the low side will drop down to approx 40psi. The shop mechanic said the compressor was bad (a new compressor) so I exchanged it for a new one. When replaced, the problem remained the same. I have sprayed water on the condenser with no appreciable drop in cooling or pressure. When I flushed the system it appeared clean and when I reflushed the condenser before installing the 2nd compressor the fluid seemed to flow out OK both on its own and with compressed air. The vendor for the AC parts said the comprressor was not pulling down was because something was restricting the flow. The only thing I did not replace was the condenser. Is there any way to check to see if it is restricting the refrigerant? Could the expansion valve be the problem (it is new as well)?

Thank you