DIY "Slushie" Machine from Portable AC Unit

`Put the output from the compressor at the bottom of the coil.Add Freon till you get about 10 degrees F of super heat.The existing capillary tube was designed for a certain amount of Freon volume.It may require more for your application,so I recommend an adjustable TXV.You may also need to add more coils to your bucket.Water has a lot more specific heat than air,so I am thinking the capillary tube is too small.

Test the super heat when the water is at room temperature,which is max load on the unit.

The load will decrease as the temperature drops,so put a receiver\dryer in the return line to catch any liquid before it reaches the compressor.A few drops of Freon will not hurt but a lot of liquid will trash the reed valves.

This is also a reason I recommend a adjustable TXV.

(You might also think about using a freezer compressor that is designed for such an application.)

A commercial ice maker runs about -10 F with 404a and it streams water over the coils which are in an aluminum sheet, the water circulates from a sump with a float valve that is located in the cool section of the cabinet, as the water gets colder and colder it freezes faster and faster, when the ice gets to about 3/4" thick a reversing valve kicks in and the panel heats and the ice sheet drops off onto a metal grid with 1" holes, that grid heats up with voltage applied and cuts the ice sheet into cubes that then drop into the bin....It takes a while to cool down before it starts producing ice, but when it does it drops ice about every 10 minutes... Commercial slushie machines take about 1 hr to freeze...but you need constant circulation...

I would just buy bags of ice and use a blender...

The slushie machines have a cylindrical evaporator with an auger like scraper...

https://www.theslushiespecialists.com.au/gbg-parts/?sort=featured&page=1

If it were me, I would find someone giving away or selling for a very low price an old refrigerator/freezer. then I would cannibalize the compressor/condensing unit and build my own coil.

Or since you are in the business, find a unit from an old walk-in unit or commercial freezer.

The second choice will chill your slush down quickly especially if you are making adult Slushies

I have a slushie machine that I purchased used for about $250 a number of years ago that uses R-22. I also am HVAC certified but I don't do it for a living, I got my certification because I purchased a broken soft serve ice cream machine and needed to purchase parts and refrigerant to repair it (it it works now). I would think R-410a would work and probably better than R-134a so I doubt switching that out will help.

On my slushie machine as shown in a picture in another post above it has cylindrical metal parts that gets cold and an auger around them to scrape off the slush. My soft serve machine is sort of reverse having a cylindrical metal tube and augers inside that but it too can take flavored sugar water but you get sorbet. This sounds closer to your design.

Not sure what kind of bucket you are using but I would be concerned about the heat transfer through plastic and even with metal to have a good thermal connection to the evaporator. My slushie machine takes about 2 hours to turn 2.5 gallons of sugar water to slush. It must just be cold enough for it to work because I found out it won't make slush if the room temperature is in the 90's. Reversing the flow through the evaporator may help for your setup. I have noticed that if I run the slushie machine without anything in it, only the end part of the cylinders get icing on them. The slushie machine has worked since I got it so I haven't messed with it or checked the pressures.

The soft serve machine has a lot more umph to it as well as requiring 210v and water cooling, each side has its own compressor and can turn a few gallons of sugar water into sorbet in about 10 minutes. I could probably turn down the thickness setting and get something approaching a slushie.

IMHO:

The reason for injecting the liquid coolant at the bottom is because the gas will tend to rise,giving a longer path for the heat to vaporize it and absorb latent heat from the surroundings.Any excess liquid will trickle down to the bottom for another trip,maximizing the efficiency of the evaporator coils.Sort of like a stack distiller.The slope of the coils is also a factor here.Not too flat,not too steep,and a larger diameter tube is better than a small one.

The ice will rise to the top inside,and the liquid,which is warmer will be forced to the bottom,like when a lake freezes over.It is warmer under the ice. This will give better heat transfer due to the larger differential temperature.The scraper will try to maintain a complete mix,but it will always be slightly warmer in the bottom,until the agitation stops.

The result should be a pure vapor leaving the evaporator.A few drops of liquid will insure that you are injecting enough Freon to achieve maximum utilization of the evaporator section.Check superheat under max load at first startup.

Do not insulate the liquid line leaving the compressor;warmer liquid will vaporize quicker.It is the latent heat that provides the cooling,not the liquid temperature entering itself.

A cylinder with a wiper is like a ice a home style ice cream machine.

I presume you intend to scoop it out manually,if so you don't need to have an auger scraper.

The auger is used to force the slush out of a nozzle.The paddle-type scrapers will work just fine in this application.An old ice cream freezer has everything you need,just substitute your copper coil for the ice in the bucket,and a ethyl alcohol or Propylene glycol liquid transfer medium.Do not confuse with Polypropylene glycol.

All of the above is simply how I would do the same task,but I do not recommend anyone try it without proper knowledge training,this is merely an opinion.