Sub-Zero Designer Code 15-3-01: Zone 3 relay closed when it should open

What 15-3-01 means

On Designer units like the DEC3050R column and DET3050CI tall model, 15-3-01 means the control-board relay that switches cooling for zone 3 reads closed. The control expects the relay to be open, yet it sees the circuit still switched on, so cooling for that zone may never stop. Zone 3 can become colder than its setting, and the unit may sound like it runs constantly. Cooling that never rests works the system harder than intended, so this code deserves attention even if food seems fine.

Common causes of 15-3-01

Relay contacts stuck closed
Electrical noise on the supply line affecting the relay sense
Control board output stuck on

✓ One safe check you can try

1) Listen for a unit that never seems to cycle off. 2) Check zone 3 with a thermometer. 3) Unplug other heavy loads on the same circuit. 4) Turn the breaker off for a minute, then back on. 5) Call us if 15-3-01 returns.

! Why to stop there

Relay testing requires measuring a live board.
Board replacement must match the Designer model.
Constant running adds wear to the cooling system.

Opening a panel yourself does not automatically cancel a manufacturer warranty, but it can cause accidental damage, and some manufacturers set their own service conditions. Check your warranty terms, or ask us, before deciding.

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15-3-0115-3-01 questions

Is a very cold zone 3 related to 15-3-01?

Yes. If the relay is stuck closed, cooling for zone 3 may keep running and push that zone well below its setting, sometimes freezing items meant only to chill.

Can electrical noise cause it?

It can on some units. Interference on the supply may make the control believe the relay is closed. We check the supply quality and the relay together.

What does the repair include?

We test the relay, the board output and the incoming supply, then repair or replace the part responsible. You approve a written price, and labor is covered for 30 days.