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Generally, low side is around 20-25 PSI and High side is about 235-250 when unit is close to operating temp. Expansion device effects this to some degree such as a cap tube can restrict and affect pressures as well as the amount of the charge in the system. Compressor efficiency is another.
sounds like you covered most all bases. without knowing pressures, I would look for a possible restriction. Since the TXV was replaced, are you sure you went back with OEM? If refrigerant was weighed in, was the drier an oversized one? It's rare but I have found some units that just don't cool right with the factory weigh in charge. You may want to try to charge by pressures. If it has a condensate pan with a hot gas line, be sure it is dry before trying as this effects the pressures. Good luck. Looking forward to hear about the fix.
Ok, basic refrigeration here. The 'high side' contains the high pressure vapor leaving the compressor and going to the condensor to condense into a high pressure liquid. The 'low side' contains low pressure refrigerant vapor within the evaporator and the suction line back to the compressor. The same amount of vapor has to return to the compressor as left the compressor. So thinking about pressure solves the problem....High pressure equals small line...
Low pressure equals larger line. The low pressure vapor will fill a larger space than high pressure vapor so it has to travel in a larger line. The suction side is the bigger of the two and if the unit is functioning, it will be the one cooler to the touch.
Though this is basically correct in theory, it is not a totally perfect way to descsribe an answer to your question, but it was fun to try.
Compressor should rapidly bring pressure down from standing pressure to running pressure when switched on. If no change, compressor not pumping. Make sure the line tap valve isn't leaking, and the gas you used was correctly charged.
Take the top cover off that is next to the compressor,. That cover is about 30 by 30 inches. You will see two fans and an evaporator coil. Several things can happen. First these fans won't come on until the coil is somewhere around 10 degrees or if the door is open. So, once the freezer has been running look under the big cover and be sure both fans are running. If one or both are not running it won't pull down to 0. Also look at the coils and see how much frost has accumulated. If your defrost timer is not working it may be frozen over. When that happens air is blocked from reaching the inside of the freezer. While you are at it, fell of the coils if they are only partially freezing, you may be low on freon. If you have gauges to check the freon charge, check both the high side and the low side pressures. If the high side is less than 200 psi, you have some freon, but maybe not enough. If the high side pressure is 300 psi, you have something blocking the freon from returning to the compressor. Usually a blocked cap tube or a malfuncting expansion valve. Finally check the condenser coils which is the radiator thing out where the compressor is located. If it clogged with dust and grease, it will not dissapate the heat from the freon and will intefere with the operation of the entire unit. Clogged condener coils are probably the number one cause of burned out compressors. Good luck.
Freezers usually have a super heat of 6-8 degrees and as it approaches the set temperature, it can be as low as 4 degrees. you will have to 'babysit' this and adjust as you go but it has to be done in extremely small amounts. the crankcase pressure regulator basically keeps the compressor from being overloaded from high pressure like from after a defrost or the door being left open.
Possibly a bad valve but more likely not enough water coming to the unit,follow the water line from the back of the unit to where it hooks to the pipes there is usually a little saddle valve there,try closing it all the way and then open it back up check the water through the door and see if the pressure doesn't improve.
You can also remove the Ice maker clear out the fill tube and sit a cup under the end of it for a day or two if you get water in the cup and Ice in the tube you probably have a solenoid valve that isn't closing completely.
I'll try to give you the "Readers Digest" version.
First, make sure there is no ice build up on the evap. Light frost is O.K. as long as it does not effect air flow. (Very Important). All fans need to be running. Again, an air flow thing. There should be some product in the box but not too close to the evap. Again, an air flow thing.
The expansion device can effect your pressures to some degree i.e. Cap tube vs. TXV.
As a general rule of thumb, which I use almost everyday when it comes to pressures:
Low side is based on the temp difference between evap temp and condition space in the box. In freezers, it is almost always 10 degrees. If the box is 0 degrees then the evap needs to be at a minus 10 degrees. That is a pressure for R-404A of 24.5 psi. This only holds true when the temp in the box is approching set temp. I would say, about +10 degrees. 0 Degrees for the evap for R-404A is 33.5 psi.
High side should be ambient temp +30 degrees and then convert to a pressure for the refrigerant.
Example: 75 degrees in the room, +30 degrees equals 105 degrees. Now 105 degrees converted to a R-404A pressure is 253 psi. This will get you very close to the desired high side pressure.
I would look at low side first to see if it is within reason. Don't let the high side get too high. Increases the compression ratio and overworks the compressor.
Your icing problem could be a defrost issue and not a refrigerant charge issue.
Most all cooling systems need to be in an ambient temp of about 60-65 degrees. If not, it needs a low ambient control. This helps keep the high side pressure high enough so you have the proper pressure drop accross the expansion device. This applies to coolers, freezers, a/c units, and so on. I also think, if it keeps things frozen like you want, where's the problem? You make have a control just acting stupid.
That system has a restriction. Most common at TXV valve or capillary tube. Will need to be replaced by Refrigeration company. In this video I replaced TXV valve and filter drier due to the same issue You have. Its Ice Machine, Low side was at 5 PSI, High at 250PSI : 404A; should be around 55-65 Low; 250 -275 High. Replaced drier and TXV, machine works proper.