Frost Building Up in the Freezer: Defrost Faults, Gaskets and Humidity

Frost on the back wall of the freezer, ice around the ice maker, a fridge section that has started running warm while the freezer is buried in snow. Owners read this as a refrigerator that is too cold. It is the opposite. Frost means moisture got in and the machine could not get rid of it, and in South Florida that comes down to three causes: the defrost system stopped working, the door is letting humid air in, or the drain that carries meltwater away is blocked. Here is how to tell them apart and what each costs.

Cause 1: the defrost system has failed

A frost-free refrigerator runs a heater under the evaporator coil a few times a day to melt the frost that normal operation deposits there. When the defrost heater, the defrost thermostat, or the control that times the cycle fails, the frost never melts. It builds on the coil until the evaporator fan is buried in ice and cannot move air. Then the freezer stays cold, because it is a block of ice, and the fridge section goes warm, because no cold air reaches it.

Tell-tale signs: a sheet of frost on the back wall of the freezer, not just around the door; a fan that got loud and then went quiet; the fridge section warming over a week or two. On Samsung, LG, Whirlpool, GE and Frigidaire the failed part is the heater, the thermostat or a sensor, $160 to $340 with labor. We thaw the coil, replace the part, and confirm the next defrost cycle runs. It is not the compressor, and the cold freezer proves that.

Cause 2: the door gasket is letting Miami in

Every time the freezer door opens, humid air enters. In a house with 70 percent humidity that is a lot of water, and the defrost system is sized for it. But a gasket that has flattened, torn, or stopped sealing at one corner lets that air in constantly, and no defrost cycle can keep up. The frost forms near the door first, on the door shelves and the front of the compartment, and it looks fluffy, not glassy.

Test it: close the door on a dollar bill and pull. If the bill slides out with no resistance, the gasket is done. A door that does not close flush because a drawer is out of its track or a bag of frozen peas is behind the shelf does the same thing. Gasket replacement runs $160 to $320. On French door units the flipper mullion between the doors has a heater, and a failed mullion heater lets the two doors sweat and frost at the seam.

Cause 3: the defrost drain is blocked

The meltwater from each defrost cycle runs down a drain at the back of the freezer and into a pan over the compressor. When that drain clogs or freezes, the water refreezes as a sheet of ice on the freezer floor, then overflows into the fridge and out the front. This is frost in the wrong place: on the floor, not the wall. Clearing and treating the drain, and fitting the revised drain part several manufacturers issued, runs $130 to $240.

Cause 4, the small one: the ice maker fill tube

Ice building around the ice maker itself, with a stalactite hanging from the fill tube, is the fill tube freezing because the fill valve drips after the fill or the tube heater has failed. On Samsung French door units the whole ice room frosts over for a different reason, a sealing problem with its own kit; that is on the Samsung ice maker page. Fill tube and valve work runs $150 to $300.

What manual defrosting does and does not fix

Unplugging the refrigerator for 24 hours with the doors open melts the frost and, if the cause was a one-time event, a door left ajar overnight, that is the whole fix. If the cause is a failed defrost part or a bad gasket, the frost comes back in two to four weeks, and each cycle of thaw and refreeze puts water where it should not go. A refrigerator that has needed manual defrosting twice has a part that needs replacing.

Reading the frost

• Glassy sheet on the back wall, fridge warming: defrost heater, thermostat or sensor, $160 to $340
• Fluffy frost near the door, door shelves iced: gasket, $160 to $320, or a door not closing
• Ice on the freezer floor, water under the crisper: defrost drain, $130 to $240
• Ice around the ice maker with a stalactite: fill tube or valve, $150 to $300

We repair every refrigerator brand across Miami-Dade, Broward and Palm Beach, seven days a week, with a $59 service call that is free when you approve the repair. Call (754) 345-4515 or see refrigerator repair. Brand pages: Samsung, LG, Whirlpool, GE, Frigidaire.