Why does frost keep building up in my freezer?

Why that is usually the answer

The reason is usually one of three: the heater is dead, the thermistor has drifted far enough out of range to mislead the control, or the control has stopped calling for defrost at all. Inland this diagnosis is cleaner than it is on the coast: dry valley air carries much less moisture, so a marginal door gasket has far less water to work with and heavy recurring frost points hard at the circuit rather than at air getting in. Once the coil furs over it insulates itself, so cooling drops a little further every week instead of failing outright.

Where it usually turns out to be

Clearing frost by hand treats the symptom and destroys the evidence. If you can stand it, leave it and call. The position of the ice matters as much as the amount of it. Frost spread evenly over the whole coil is a defrost failure. A thick patch built up in one corner by the door is a seal or a hinge sitting out of line. A clean coil with ice lying on the floor of the compartment is a blocked drain and nothing to do with defrost at all. Ten seconds with the door open, before the scraper comes out, is often the difference between one visit and two.

What we check: heater resistance measured cold; thermistor resistance against the model's own curve; a forced defrost watched right through to the end, because a heater that works for two minutes and quits reads perfectly fine on a meter; the drain path, since melt water refreezing at the outlet rebuilds the whole problem within days; the evaporator fan for blade contact; and gasket pull along the hinge side, where heavy doors lose their seal first. Then cabinet temperature at the coil with a calibrated probe rather than whatever the display would like to tell you.

If that matches what yours is doing, say so when you call — it decides which parts come on the van.

Questions

Frequently asked questions