Something is drifting
The unit holds, but not like it did. It runs longer, the display sits a degree higher, the alarm goes off once a week, one shelf is warmer than it was. This is a service call before it becomes a repair call. The mechanic looks for the reading that has moved: a charge a few percent low, head pressure creeping up, a fan motor drawing more current than its nameplate, a probe two degrees off, a defrost element gone out of four. The moved reading is named and the component behind it is repaired while the equipment is still holding.

