The honest answer is that 'once a year' is a marketing interval, not an engineering one. The correct frequency depends on three measurable things: how hard your water is, how close the machine runs to its rated capacity, and how clean the air around it is.
Hard water shortens the interval
Scale on the evaporator plate insulates it. A machine on untreated borehole water can lose noticeable output within three to four months, while the same machine on well-filtered municipal water may hold output for a year. If you see white deposit anywhere in the water path, your interval is too long.
Load matters more than age
A canteen machine running at ninety percent of rated capacity every shift wears its pumps, valves and contactors several times faster than a guesthouse machine that fills a bin overnight. High-load sites usually settle on quarterly service; low-load hospitality sites often manage on six-monthly.
Dirty air means condenser attention
Kitchens with heavy frying, plant canteens and warehouse sites foul condensers quickly. On those sites we often split the work: a short condenser clean between full services, and the full clean, descale and sanitise at the longer interval.
A practical starting point
Quarterly for high-volume canteens, food processing and hard-water sites. Six-monthly for typical restaurants, bars and hotels. Then adjust based on what the first two services actually find — measured output is a better guide than a calendar.