How Defrost Is Supposed to Work
A frost-free unit periodically warms the evaporator with a defrost heater, melts the frost, and drains it away, all on a timer or adaptive control. When a heater, thermostat, sensor or control in that chain fails, frost accumulates on the coil until airflow chokes and cooling suffers. So frost buildup and a warming compartment often arrive together.
Common Causes and What We Check
| Symptom | Likely Cause | What a Technician Checks |
|---|---|---|
| Ice on the back wall | Defrost heater or thermostat | Heater continuity, defrost cycle |
| Frost plus warming | Evaporator buried in ice | Coil, defrost components, airflow |
| Frost near the door | Worn or loose gasket | Seal and door alignment |
| Water with frost | Clogged defrost drain | Drain and trough |
Notes by Brand
Sub-Zero: On built-ins a failed defrost heater lets the evaporator ice over behind the rear panel, which shows first as frost and then as a warm fresh-food side. Symptom-based diagnosis.
Thermador and Monogram: These columns may log a defrost or sensor fault we confirm on the control while checking the heater.
Viking and True Residential: Defrost thermostats and drains are the usual culprits, with no numeric codes to lean on.
Liebherr: A temperature alarm can accompany frost when the coil is icing and airflow drops.
Frost Is a Symptom, Not Just a Nuisance
Because ice on the evaporator eventually blocks airflow, treating frost early prevents the follow-on call about a compartment that will not stay cold.
When to Book a Repair
If frost returns after you clear it, a defrost component has failed. Book a refrigerator repair and we will test the heater, thermostat and control.
Frost Keeps Coming Back?
Book a visit. Diagnostic and travel fees, if applicable, are confirmed before the appointment and before repair approval.