Not Cooling · sign 4 of 6
A Knock or Shudder Each Time the Compressor Stops
A single knock or shudder each time the compressor stops points to the compressor, its mounts or the tubing around it, and the diagnosis decides which.
Sub-Zero Repair Sammamish · (425) 610-8986 · $89 service call, credited
- Compiled by
- Marta Fennimore
- Holds
- EPA 608 certified
- Dated
- Years at the work
- 12
What you notice
The hum fades and a thump follows, every cycle
The unit runs quietly, the compressor's hum dies away, and then comes one dull knock or a short shudder you can feel through the cabinet front or hear across a still Sammamish kitchen at night. It does not rattle while running; the sound belongs to the moment it stops.
It may have begun suddenly or crept in over weeks. Either way it repeats with each cycle, which sets it apart from the occasional sizzle or crackle Sub-Zero describes as normal while a freezer defrosts.
Sub-Zero Repair Sammamish · (425) 610-8986
What it points to
Something shifts as the compressor comes to rest
The compressor is a motor-driven pump, and each time the control switches it off it has to come to a stop. It sits on mounts meant to absorb that movement, with copper tubing linking it to the rest of the circuit.
A knock at that moment can come from a mount that has hardened or shifted, from tubing that now touches a bracket or the cabinet, from a loose part close by, or from inside the compressor itself. Some of those are small fixes; the last is a sealed-system question.
Nothing heard from outside the unit tells them apart, which is why the diagnosis comes before any figure.
Sub-Zero Repair Sammamish · (425) 610-8986
Safe checks
What to note before anyone lifts the grille
These take a few minutes of listening and a look around the unit; no panel comes off.
- Time the knock
Note whether it comes as the hum stops, as it starts, or at random, and roughly how often in an hour.
- Open the doors when it happens
Sub-Zero's noise guide has owners open all doors to find out whether a sound stops; note whether the knock changes.
- Check nothing rests against the unit
Items on top, a leaning cabinet door or trim pressed against the unit can turn a small movement into a loud knock.
- Clear the front of the grille
Move anything stored against it so the condenser gets its air and nothing touches the unit's face.
That is where an owner's part ends. Panels, wiring and refrigerant are a technician's work — Sub-Zero Repair Sammamish, (425) 610-8986.
When to call
Call when the knock is new, louder or comes with warmth
A knock that has only just started, one that grows louder from week to week, or one that arrives with a warming cabinet deserves a technician's ear. Mounts, tubing clearances and the compressor itself all sit behind panels, and telling them apart decides whether the job is a small one.
When you book with Sub-Zero Repair Sammamish, describe exactly when in the cycle the knock comes. The $89 service call is credited to the repair.
Sub-Zero Repair Sammamish · (425) 610-8986
