Why is my wine cooler not holding temperature?

The reasoning behind that

On a dual-zone column, one zone steady while the other climbs clears the compressor and the condenser and puts the fault in that zone's own evaporator, fan or damper. When both zones read correctly and the wine is still warm, the question is air distribution: racks packed tighter than the design allows, or on undercounter cabinets a base grille closed off by the bar joinery the unit was built into.

How the diagnosis goes

Two degrees means something on wine that it does not mean on food, and the contents of most of these cabinets cost more than the cabinet did. So the probe goes to the top rack and the bottom rack separately, on single-zone units as well as dual. A cabinet that is accurate at its sensor and four degrees warm at the top has an air distribution problem, not a refrigeration problem, and that is a different repair from anything involving the sealed system. It also explains how a cabinet can pass every self-check its electronics run and still be slowly cooking a collection.

The undercounter cabinets here were installed to vanish, and that is what breaks them. They take air in at the base and reject heat there too, and a continuous decorative toe kick, a return panel or a stone detail added after the appliance was chosen will shut that path completely. The unit then runs its compressor without pause, never reaches setpoint, and presents as a failing machine. We measure the clearance it was designed to have before condemning anything inside it, because no part fixes an appliance that cannot get rid of its own heat.

If that matches what yours is doing, say so when you call — it decides which parts come on the van.