Bunn Ultra-1 (single bowl version of Ultra-2) Refrigeration Questions

[JLJeff]

Hello,

I've recently acquired a Bunn Ultra-1 slush machine that I'm having some issues with.  The machine will freeze, but takes a very long time.  Like 5 hours or more.  I've had a tech look at it as when I initially got it there was no refrigerant in it. He pressure tested and evacuated it, and it seemed to hold both pressure and vacuum for several hours.  So he weighed in a 6oz charge of r404a which is what is specified on the label to be the proper charge.  However while I now get cooling and hot air coming off the condenser, it's atill struggling to actually freeze the product. 

I've tried a few things to troubleshoot...the latest being removing the solenoid coil and placing a test magnet on to make sure the valve is staying open.  The reason I suspected the coil may be weak was because if I would apply and remove voltage from the coil at 30 second intervals I would be able to get a slightly colder evaporator temp. 

While it might be freezing a little better with the magnet on (and my evap temp seems a little lower..now at 26 to 27 degrees vs a steady 28 when the coil was on the valve) I'm not so sure that's the issue. Since it's still not really working correctly and taking an exceptionally long time to make slush.

I've also noticed the hot gas temp is relatively cool...at least forn what I think it should be.  It seems to settle between 74 and 76 degrees...and not really go any higher except for when it's 1st started.  And the other thing I noticed is the compressor body remains cool to almost cold to the touch.  Now pretty much any other appliance I've ever worked on the compressor is warm to hot...including a different slush machine I had prior to this one. For anyone familiar with the bunn machines there is a temp & torque display that shows the evap and hot gas temps...thats where my numbers are coming from.  The compresor body is roughly 52 to 55 degrees taken with an IR thermometer. And by feel it's cool to cold to the touch.  

My questions are...what could be causing these symptoms?  Would it be low on charge again already?  I feel like that would have the opposite effect..as usually the evap temp is too low at least initially until it is nearly empty.  Is it overcharged? I once serviced a window ac unit that had a cold compressor that was way overcharged and after correcting it the compressor case was warm and it worked normally and still does.  He said he weighed the charge in from a vacuum so it shouldn't be overcharged...? 

I'm kind of at a loss with this one.  Restriction?  Bad compressor?  Condenser fans too strong?  

Any ideas anyone can toss out would be appreciated.  And it's not that I won't have a pro look at it...I'm having no luck finding anyone because they seem to only want to service businesses that have machines under a contract.  I've contacted at least 6 places and no one will service it for me. The tech I did have look at it is a certified hvac and refrigeration technician with the proper tools...but he's not an ice machine or freezer tech so there could be something he missed or did incorrectly that may be proper for medium temp refrigeration but maybe not low temp?  I too have serviced many air conditioners but never a freezing device so this one is a bit above me to figure out. 

Thanks,

Jeff

[JLJeff]

Nobody has any thoughts on this?  Dang.