Why is my Sub-Zero refrigerator not cooling?

What is actually going on

These built-ins run one sealed system per compartment, so a freezer still holding hard proves the costly half of the machine is fine and drops the fault squarely on the refrigerator circuit: its own evaporator fan, a defrost failure that has turned the coil behind the rear panel into ice, or that circuit's thermistor reading the cabinet wrong while the control obeys it. Both compartments going warm at the same time is a different problem entirely, and in Cardiff it is the condenser more often than not. Salt air binds dust into a mat across the fins, the coil stops rejecting heat, and the unit runs long through the afternoon and catches up overnight.

What we check, and in what order

The order we check things in is deliberate, and it goes cheapest and likeliest first. With a cold freezer and a warm fridge: is the evaporator fan on the refrigerator side actually turning, is there ice on the coil behind the rear panel, is that circuit's thermistor reading the cabinet correctly, and does the door gasket still pull along its whole length. Between them those four cover the majority of the calls we take here, and none of the answers is an expensive part. Nothing about a warm refrigerator with a working freezer suggests a compressor, and anyone who quotes you one before opening the rear panel has not looked.

With both compartments warm, we start at the lower grille. A condenser out here does not look like an inland condenser. The loading is not a layer of fluff that lifts off, it is a dense film worked down between the fins that has to be combed out. While the grille is off we check the condenser fan, because a fan running on a corroded bearing is the most common precursor to a genuinely expensive failure in this town. It gets louder for months, then it seizes, and after that the unit is rejecting no heat at all.

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