I've just joined this great site and this is my first post. I've come across this heat pump that has me absolutely stumped. First of all some background. This is a four-year-old York condensing unit (3 phase) with a Lennox indoor unit and a York coil replacing the original fitted with a Danfoss TXV. The condensing unit is one story above the evaporator and there are no risers or traps. This is R-22 by the way.
When I first was called to this job, I found that the compressor had burned out (open windings). I was able to get a warranty compressor, which I then installed. I cut out the original filter/drier, as well as an external one and installed a freshie. I pressure tested, vacuumed and recharged. When I hit the power, it took about 10 seconds for the low side to go into a vacuum. I thought, "great the TXV is plugged", but somehow I just didn't buy it. To test this I recovered the gas, valved off the lineset and sent nitro through the high side only. Sure enough my low side guage rose right along with the high side. But as a matter of practice, I replaced the TXV to totally eliminate that possibility. The new TXV made absolutely no difference.
I tried the unit in heating and it basically goes into a vacuum as well. In heating, the low side king valve port reads about 250 psi, the high side king valve port reads about 110 psi and the low side suction port reads about 20 psi. There must be some kind of restriction, but why does nitro fly through with no problem and there's no evidence of any oil slugging. Anyone encounter anything similar to this?