For me anyways. I'm new to the field, Started in October of last year down here in South Florida (for those who require a basic introduction before soliciting advice). Last December I worked on a 404a walk in freezer that had blown the start and run caps from drawing high amps. the Filter drier was installed backwards as well. After recovering charge and replacing caps and repairing burnt off compressor wires, installing new Liquid Line Filter drier (in the proper direction), pulling a vacuum on the system, I went to charge the unit up again and found that my head pressure was through the roof and the sight glass was bubbling. Suction pressure was sitting steadily at 25-30psig and Head was at 325 or more. Compressor was rated at 8.2 amps and was drawing around 9. I figured it was the TXV or Liquid line solenoid clogged by some rougue filter drier dessicant, but it was getting late so I removed enough charge to get the unit limping along without drawing over the full load amps. Yesterday got a call (yes I know the problem was never actually solved the first time but the customer never compained again until yesterday.) the freezer was down. Caps blew up again. did some more diagnosing and with the high superheat at the evaporator and high head pressure I was certain the valve needed to be replaced. Today I replaced the valve and the same problem came about. I purged the liquid line before I brazed the valve in (opened up the liquid line solenoid as well to do so), pulled a vacuum on the entire system, put virgin refrigerant in and got it running 35psi/325psi. Bubbles in the sight glass, any addition or reduction in charge did not change the suction pressure, just head pressure. Checked the liquid line temperature at the condenser all the way to the TXV inlet with little temperature change, essentially ruling out a clog. The box was hot when I started it but the head pressure never wavered from 325. Liquid line temperature was sitting at 115-112 the entire line from before the filter drier to the inlet of the TXV, much too high for my liking! Subcooling was around 8-9 degrees F. TXV appeared to hunt. Evaporator outlet was running a steady 15 degrees even after about 5 turns counter clockwise (not consecutive and as a last resort) of the superheat adjusting valve to lower the superheat. My only theory would be that I have a giant bubble of nitrogen stuck in the system to create the high head, but I pulled a vacuum and the liquid line port is on the top of the receiver! My only other theory is that the condensing unit is terrible undersized for the operation. Compressor is a Tecumseh model number AWA2460ZXD and evaporator is an American Panel model number QALH1557. Any wisdom would be greatly appreciated.