Can you define new here? Is it an actual new unit, a parts store rebuild new? I ask because oftentimes parts store rebuilds were rebuilt by soaking it in cleaner and shipping it back. I've had so many bad rebuilds over the years that I don't even bother with them anymore. If you have AC gauges, which I assume you have if you have a vacuum pump, it should show no pressure across the high and low pressure gauges, but running it should be within the readings on this chart. There's also a short list of possible problems according to the pressures you see.

This just occurred to me - when you changed the unit did you flush the parts you didn't replace with HVAC cleaner? When a compressor goes bad it can throw a ton of trash into the lines. If not you may have fried your new parts with crud from the old compressor.

 

So you did pump the system down and hold a vacuum for a bit before charging the system? How much refrigerant did you put in? Too much and there won't be a pressure drop. That's how the temperature is changed via phase change from liquid to gas. Did you use manifold gauges or just an cheap charge kit?

 

Right now, the most important question to answer is:
Did you pump down the system with a vacuum pump?

Second:
Did you replace the orifice tube?

 

1. Orifice tube is probably plugged. 2. Take it to a professional who has all of the right equipment to service the system correctly. My system would gradually warm up and be like luke warm until I shut the system off and restart it. Orifice tube was pretty plugged up.