Hi.. let me see if I can help.. this unit does not appear to have a defrost timer... also since you indicate the shutdown is random.. I would probably guess you may have issues with the metering in the refrigerant lines... its possible that there is some sort of debris in the refrigerant that clogs the metering device (cap tube) and causes the unit to go out on hi pressure... once the unit shuts down and the pressure equalizes, the compressor comes back on... the fix would be to have a refrig tech put guages on the unit and observe pressures and run characteristics for 24 to 48 hours... usuall we do it at our shop... if what I suspect is true, then they would need to vacuum the system, possibly replace the cap tube and refill with refrigerant....
Let me know what you find so I can help further...
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. I would think if it was a clog, not sure what the debris would be? the compressor would still run? What would cause the compressor to shut off. paid $2100 for unit 3 years ago,
Diagnostic by tech $ 250, 150 to walk through the door, $500 to change cap tube pus the refrigerant, at less $900. is there anything else it could be. still paying for original purchase.
compressor will run until enough pressure is belt up to shut it down on overload... the debris can be flaking metal particals from the tubing... or from moving parts of the compressor... the metering device is a very tube that has a very small oriface for the refrigerant to pass.
Like I said... that is my best guess... but since it is random.. only a tech on site can possibly see it happen... commercial equipment is expensive and expensive to repair.... we charge 98 hour plus 30 truck charge just to walk in the door too...
there are only a few parts to this equipment... none would cause the compressor to stop other than the compressor itself.. ie overload or overtemp... or start run components... the tech can determine if the compressor is failing or something is causing the compressor to stop running... when was the last time the evaporator and condensor fins ( not fans) were cleaned..?