I love a good challenge and the chance to learn something new. But this one was ridiculous.
With the correct charge weighed in the suction would pull into a vacuum after about 30 seconds and the head pressure would run about 270 psi.
Now this is a new house. First time the A/C has been run.
After over charging the system enough to get some suction pressure returning to the unit I was able to check the line temperatures inside and out. Only the usual 2-3 degree temperature difference. By this time the pressures were 650/125. So I did not let it run very long like that. Replaced the TXV at the indoor coil. While it was apart I blew through the line set with plenty of nitrogen. no problems. Put it back together....Same problem.... Next I ran a temporary new liquid line down the attic access hole and out a window to the outdoor unit....Same thing... By this time I'm getting pretty frustrated. Finally I pulled the evaporator and brought it outside. Sat it on top of the condenser and piped it in. Finally it worked. Now came the hard part. Replacing a 90 foot line set in a fully finished $500,000 house.
After all day the new line set fixed the problem. How ever I was never able to locate a problem with the line set I pulled out.
Just a side note. The line set I pulled out was aluminum.