Behind the kickplate Part 2 of 3 in this group
Compressor and Start Relay on Small Units
The pump that makes the cold, and the small start parts that get it running.
The compressor is the part owners fear first and the one we condemn last. On Mercer Island, where remodels set wine and undercounter units deep into joinery with only a toe-kick to breathe through, it is more often the victim of trapped heat than the cause of a warm cabinet.
Why it comes last
A compressor starved of air runs longer and hotter. Sub-Zero’s undercounter guides note that warmer surroundings lengthen its running time, and warn that a condenser left dirty can end in mechanical failure. So it is judged last, after the coil, the fan, the door, the control and the start parts.
The start components
A compressor motor needs help for the first moment of each start. A start device on the compressor’s terminals, often called the start relay, feeds the start winding a brief surge and then drops out of the circuit. The hardware differs between models.
When starting fails, the sound is familiar: a hum from the base, a click, silence, then another attempt after a pause while the cabinet warms. The click is the overload cutting out a motor that could not get going. The cause may be a failed start device, low voltage at the outlet, heat from a clogged coil, or the compressor itself, and the meter decides which. A unit that starts, cools briefly and stops again every few minutes is a neighboring complaint, covered in the note on short cycling.
Sub-Zero describes the compressor in its wine storage as quiet. A new knock, rattle or harsh hum from the base is worth reporting, and the note on noise in an open-plan room separates the ordinary sounds from those that need a visit.
Warranty and the sealed side
Sub-Zero’s warranty counts the compressor as part of the sealed system, with the condenser, evaporator, drier and connecting tubing: parts and labor for five years from installation, then the covered parts alone through year twelve. Inside the first five years that work runs through Sub-Zero’s own service network, so check the installation date first. On current Designer undercounter models the refrigerant is flammable, and Sub-Zero limits work on the circuit to technicians trained for it. Outside warranty, start-part and sealed-system work are priced after the diagnosis as wine storage repair.