I have a hoshizaki km 255bah compressor start then quits

any beeping? beeping says what problem it is having.
Reset it while energyzed by pushing the button way back of the control board in the control panel section.
The switch needs to be set to run and valve to normal position, full ice bin sensor may be stuck to full position, exercise the sensor flap.
Post what you tried to remedy the situation for better help ideas. Trouble shooting instruction are included on the machine cover doors.

Is it making ice? Frost on this line is not that uncommon as it is colder than the air around it. Make sure you have good water flow over the evap plates. machine may just need a good chemical cleaning.

if your are referring to a harvest cycle not clearing the plates, there may not be enough heat to clear the plates or the defrost cycle is too short. Usually the first thing to check. start there my friend.

This is a "defrost too long" code. Look for bad thermistor or low refrigerant charge first as these are the easiest and most likely place to start.

Well aside from jacking the machine up and putting another in its place, the only thing left is the electronic thermometer/thermostat that should be sensing the ice and not the outside temperature. By the way, if you spend more than the machine is worth think about another one.

really sounds like the board needs replacing. after 1 minute, if the float is doing it's job, the compressor is to come on provided the water level is correct and the float is doing what it was designed to do.

http://www.hoshizakiamerica.com/manuals/KM-900M_F_inst.pdf
This is the manual for your machine. Check out the pages that have examples of the nameplate information. It shows that the machine is approved for UL and NSF. Otherwise, I would suggest contacting Hoshizaki directly.

Check the compressor and it capacitor.They may damage

when the machine first starts, it begins it's cycle in the harvest mode. If the float switch is stuck, it stays in the fill/ harvest mode. Compressor runs and water circulates but no ice is being made. I'd start looking there. Turn the machine on, let it run for about 3 minutes, they very lightly tap the float switch. If it starts making ice, bingo, theres your problem. Let me know if I can be of any more help.

put an amp probe on common wire at compressor and see what amps are when it tries to start. 40 to 60 is mechancially locked up compressor. kill power and test start and run capacitors. there is an thermal temp over load on the compressor that opens when comp gets hot from trying to start. gently remove and look for cracks or burned looking. . i saw one this week doing exact same and i have ordered the oem compressor start cap realy and run cap and drier and will put in all new gas. be sure to allow sufficient time when switched to ice for it to get to ref cycle, it may take 5 minutes starting with water purge, then fill, etc. good luck, call hoshizaki dist they are usually pretty helpful if you need a auth service rep in you area. i think they are three years warrantied!