here is the story. 18 years ago, I installed a walk in freezer. Evap and condensing unit rated at 9000 btu's at -30 degrees. R-502 was the refrigerant.Everything working well and box holding at -12 degrees. We did have the ocassional electrical problem and even replaced the compressor once. The condensing unit is remoted in a room @25' away. Now, a year ago, the compressor failed electrically . It was replaced with a new one rated the same but using R-404A. Box began to loose temp. First it would maintain 0 degrees and and kept loosing a little until +20 was all it could do. In the mean time, the txv was changed, twice, and they had been adjusted and tweaked many times. No ghange in box temp. could be made. Always +20. The load that goes in is frozen meat at -12 . Nothing warmer ever goes into the box. It is supposed to be a holding locker. Customer says, put in a new compressor and evaporator and get over with it already. I get a new direct Bohn replacement evap. and copeland compressor and txv. Installed them. Everything is rated as it was from original but ofcourse new updated equipment. Started everything up and +20 is all I can get. Today, box at +22 and subcooling at 10 degrees, suction pressure at 22psig at compressor and suction line temp at compressor is +46 degrees. Bohn said open txv wide open and let run until box temp starts to fall then slowly adjust back to
+15 to +20 degrees super heat at compressor.Opened valave and got 30psig for just a little while the n dropped to 22psig. closed txv 1 turn and pressure did not change but box dropped 4 degrees. Not enough! Why won't this thing work? The txv is a sporlan SBFSE-A-ZP.Also the correct orifice was installed in the evap.Bohn coil is a LET090BK. Condensing unit is rated for the evap and box temp and size but do not have the numbers in front of me. Have tried everything I can think of. Lines are suction = 1-1/8 and liquid 3/8. Suction reduces to 7/8 at evap and condensing unit connections. About 25 feet long. What is so puzzling is this thing worked for many years as R-502 with no problems. I have had 9 degrees diff. from outlet of txv and out let of evap. Have measured super heat at evap. at +6 degrees. Nothing that is tried makes a difference.4 defrosts a day at 1/2 hour each and coil clears nicely. Evap seems to frost evenly in all 3 circuits. Thanks for any help.