Suction pressure on minus 40 chest freezer using 404a refrigerant

The ideal suction and discharge pressures for a Flex Ice Machine using 404a refrigerant can vary depending on several factors, including the ambient temperature and the load on the machine. However, here are some general guidelines: Suction pressure: The suction pressure should typically be in the range of 30-45 psi (pounds per square inch) for a 404a refrigerant system. This pressure corresponds to a saturation temperature of around 20-30°F (-6.7 to -1.1°C). Discharge pressure: The discharge pressure should typically be in the range of 225-250 psi. This pressure corresponds to a saturation temperature of around 100-110°F (37.8 to 43.3°C). It's important to note that these are general guidelines, and the ideal pressures can vary based on the specific conditions of the system. It's also important to ensure that the pressures are within the manufacturer's recommended range, as pressures that are too high or too low can indicate a problem with the system. If you are experiencing issues with your Flex Ice Machine, it's recommended to consult a qualified technician for assistance.

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.

It sounds like its doing good.

evap temps usuall run 10-15 degrees below the box temp.This a generally accepted rule of thumb.

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.

as long as you recovered the charge, pulled a vacuum, changed the filter/dryer, and added the correct amount of refrigerant as a liquid, you should be good to go.

why yes there is. Generally speaking, the head pressure should be around the "ambient +30" rule.
That is, measure the entering air temp to the condenser, say 75 degrees. Now add 30 to that and get 105 degrees. Look at a P/T chart and see what the pressure is for that temp which is about 253 for R-404-A.
The evap on a freezer leads the load so, as a general rule, the evap temp is going to be around minus 10 degrees to get a 0 degree box. Coolers are different. So, the pressure for a minus 10 evap is around 25 or so. But the unit has to be close to operating temp. If the box is warm, naturally the pressure is higher. And what influences the pressure is whether or not it's a TXV or a cap tube system.
If a TXV and no receiver, charge by subcooling. If a receiver, fill by sight glass. If Cap tube, charge by superheat.
Hope that answers your question.

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.

Good Luck and hope this gets you started.

Normal operating pressures will change as the freezer reaches the selected temperatures on the inside. Normals of minus 14 degrees on the inside would be around minus 4 psi on the suction and 150 pis on discharge. Now checking the pressure will require a set of guages that have been purged with the same freon before connecting with the suction line on freezer. If not purged the suction line will draw outside air into the system and cause freezing of air and moisture inside the capillary tube rendering the freezer inoperative, Hope this helps, Sea Breeze