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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.
I guess you are changing the compressor on this unit, normally if you wish to check the circuit is clear you would attach a 1/4" shraeder stub to the discharge tube with the compressor removed and use OFN at around 200psi and see if it comes out of the suction tube (it will be a gentle flow). If you get no flow the 2 obvious areas are
1. Filter drier, this should be replaced as a matter of course during a compressor change.
2. Blocked capilliary tube, there are a couple of capilliary cleaners on the market but unless you are going to do this often you may be better buying a new capilliary from your Kenmore dealer.
Once you are satisfied that the circuit is clear then refit the compressor with a shraeder stub and leak test with OFN to 13 bar (200psi) for 30 mins, release the OFN from the system then connect the vacuum pump and a Torr or Vacuum guage, you need to get to 5 torr (-29.5inHg) for at least 30 mins. Then add the correct weighed charge of refrigerant.
Sounds like a restriction to me. Recover the charge. Pressurize the system with 350 pounds of nitrogen pressure through the high side. Leave it pressurized for 15 minutes. Release the pressure through the low side. Replace the filter drier again. Pull a 2 hour vacuum on high and low side. Recharge liquid refrigerant on the high side. Let the system sit idle for 30 minutes before starting. Check the evaporator fan motor as well as the coils. Use a good coil cleaner on the e-coil.
Good day, They do a good job of hiding them, but it should be in the machine compartment near the compressor. Not too hard to remove, but you must use caution, in removing the long skinny capillary tube that is inserted into the tube that runs into the cabinet. NO, IT IS NOT A WIRE. It carries a small refrigerant charge inside and if broken, the control is ruined. Note: My experience, is the problem is a small loss of refrigerant charge in 90% of the cases, not the thermostat. If the thermostat will not shut off, and the unit runs for in excess of 24 hours, the interior temperature should be colder than -10 degrees. Check first. The purpose of a thermostat is not to turn the machine on, it's purpose is to turn it off. If the freon charge is low, it will not reach the sensing capillary tube of the thermostat described above.
The McCall web site has nothing easily found on the 7-7045FT unit.
In answer to you questions, first, what is the expansion device. TXV, Cap Tube, or something else?
Low site pressure will be dictated by the super heat. The high side, in many cases, is usually ambient plus 30, then convert to psi.
Let me know if you need more info. And please double check the model number/ serial numbers.
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.
Check out "victory-refrig.com" for manuals, diagrams, etc.
Cap tube systems are "critical charge systems". Can be difficult to get right. You did not mention pressures that you had. The split on the evap vs.box temp is almost always 10 degrees for freezers. If you want a -10 box, your evap needs to be -20. As a general rule of thumb, you want the high side to be "ambient +30". This seems to work most every time. Your problem might be operations related. Them leaving the door open alot and so on. It could also be a problem with the evap fan or the control to it. It could also be that since there had been a problem with the unit, they are now constantly checking it. Could be checking during a defrost cycle. When your box is at 0 degrees, your pressure should be about a -10 and no less that a -15 degree for the evap. You may have to babysit this thing and see how far it will pull down. You may have a weak compressor. Also, I have had many Hobart freezers fail due to dirty condensers. This causes the oil in cap tube systems to gel and clog up the cap tubes. The only fix is replacing the cap tube. There are alot of variables here so be patient, it's not going to be a quick fix. One last thing, since R404A can fractionate, you really need to pull the charge out and weigh in the correct charge with virgin refrigerant. This will eliminate 2 things. 1, it will ensure the correct amount of refrigerant and, 2 no chance of having a poor mixture of refrigerant in the system causing inconsistant readings and performance.
Hope this helps. And remember, cap tube systems are performance measured by the amount of superheat just prior to the unit making temp and cutting off.
Marc is correct, you should check to see if you have a blocked filter (this should always be changed when a system is vacuumed and refilled) or you may have oil in the line(s) causing the blockage. But you should know that there is a blockage because your low side pressure will be lower than it should be or in a vacuum and your high side pressure will be much higher than it should be. The blockage could be oil, or a plugged filter or even moisture in the system which will freeze at the end of the capilliary tube in the evaporator which blocks the flow of the refrigerant. But if this was the case the freezer would start to cool down but only for a short time from first start-up then warm up as the capilliary tube plugs up with the frozen moisture. I would suggest that you remove the refrigerant, purge the system to be sure there's no oil etc int he lines, remove the old filter and install a new one, put the system into a deep vacuum for several hours, refill the sytem with the correct amount of refrigerant and monitor it to see if there's a change. Good luck
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