A frost-free freezer is not actually frost-free. It makes frost on the evaporator coil constantly, then melts it away several times a day with a defrost cycle. You never see that happen, which is exactly the point. When frost starts showing up where you can see it, on the back wall, packed around the coils, or creeping across the freezer floor, the defrost cycle has stopped doing its job. Left alone, the frost thickens until it blocks the airflow the whole unit depends on, and then the fresh-food side starts warming too. In a Evergreen home the drier mountain air slows this a little, but a failed defrost part will still ice a coil solid within days.
Most Common Causes
- Defrost heater failure: the heater that melts coil frost has burned out, so frost never clears.
- Defrost sensor or bimetal: a failed sensor never tells the control to run a defrost cycle.
- Defrost control or timer: a bad board or timer skips the cycle entirely.
- Worn door seal: a leaking gasket lets humid air in that freezes around the opening.
- Frequent door openings or a propped door: repeated warm-air entry overwhelms the defrost cycle and frosts the coil.
Notes by Brand
Where the fault usually sits depends on the brand:
- Sub-Zero: built-ins and columns use a microprocessor-controlled defrost that must be tested in sequence, and a single failed heater or sensor is a common cause of coil icing.
- Wolf and Viking: refrigeration defrost is diagnosed by symptom, so we test the heater and sensor directly with a meter.
- Liebherr and Thermador: these often flag a defrost or temperature alarm that helps confirm the cause before parts are ordered.
- Miele and Monogram: a defrost control fault can stop the cycle, and the display usually indicates a problem.
| What You See | Likely Cause | What the Fix Involves |
|---|---|---|
| Frost packed on back wall or coil | Defrost heater or sensor | Test and replace the defrost part |
| Frost plus warming fresh food | Defrost failure choking airflow | Clear the coil, repair the defrost circuit |
| Frost only around the door | Worn door seal | Replace the gasket |
| Ice on the freezer floor | Blocked defrost drain | Clear the drain path |
Safe Checks Before You Book
Check that the door closes fully and the seal grips a slip of paper all the way around. Make sure nothing inside is blocking the vents or holding the door ajar. If you can, note whether the frost is on the coil, the back wall, or just around the opening, since that points to different parts. Do not chip at the ice with a tool, which can puncture the coil.
Frost Taking Over the Freezer?
Book a diagnosis and we will test the defrost circuit and seal. Diagnostic and travel fees, if applicable, are confirmed before the appointment and before repair approval.
Related
Not Cooling
When a defrost fault warms the box.
Temperature Swings
Icing that restricts airflow.
Refrigerator Repair
Defrost and sealed-system work.