The Sub-Zero defrost system periodically warms the evaporator to melt frost, then drains the water to a pan in the mechanical compartment. Its parts are the defrost heater, the defrost sensor/thermistor, the control's defrost logic and the drain path. When any of them fails, frost blocks the evaporator and cooling stops.
What It Does
All frost-free Sub-Zero units defrost automatically. The control turns on a heater attached to the evaporator, monitors temperature with a sensor, and ends defrost when the coil is clear. Meltwater flows through a drain tube to a pan, where condenser heat evaporates it.
Symptoms of Failure
- Frost on the back wall
- Iced evaporator visible behind the panel
- Fan ticking or scraping
- Water under crispers or on the floor
- Compartment slowly warming over days
Why It Fails
- Heater element burns open
- Sensor drifts or fails
- Drain freezes or clogs
- Control fault
Diagnosis & Replacement
We test the heater resistance, sensor readings and control defrost operation, clear and flush the drain and check the drain heater where equipped. After replacement we confirm a full defrost cycle completes.
In stock: we carry common Sub-Zero parts on our service vehicles, so most sub-zero defrost system repair repairs are completed on the first visit.
Typical Cost
| Repair | Typical range |
|---|---|
| Defrost heater / defrost sensor repair | $395 – $745 |
| Defrost drain clog / leak repair | $225 – $425 |
Typical totals for parts and labor in the Las Vegas area. The $75 service call is credited toward your repair, and every repair is backed by a 1-year parts and 180-day labor warranty. Your exact price depends on the model, the part and access, and you approve a firm quote before any work begins. Full price list →
Need a Sub-Zero Specialist?
$75 service call, credited toward your repair · 1-year parts · 180-day labor warranty · EPA 608 certified · Mon–Fri 8am–7pm · Sat–Sun 8am–4pm