Why is the Evaporator Coil Icing Up on My True Walk-In Freezer?

A solid block of ice forming on the evaporator coil of your commercial walk-in freezer is one of the most common—and potentially catastrophic—issues a facility manager will face. When the coil freezes over, airflow is completely blocked. The system will continue to run constantly, driving up your energy bills, but the box temperature will rapidly rise, putting thousands of dollars of perishable inventory at risk.

If you are dealing with an iced-over evaporator in the Portland Metro Area, you must act quickly. Here is a technical breakdown of why this happens and what you can do about it.

The 4 Primary Causes of Evaporator Icing

1. Defrost Cycle Failure

Commercial freezers (unlike coolers) require mechanical or electric defrost cycles to melt the natural frost that accumulates during operation. If the defrost heater element, the defrost termination switch, or the time clock fails, the frost will compound into a solid block of ice over a few days.

• The Fix: A certified technician will need to force a manual defrost and meter the heater elements and termination switch for continuity.

2. Low Refrigerant Charge (The Silent Killer)

It seems counterintuitive, but low refrigerant causes icing. When the system is low on Freon (due to a leak), the pressure drops. Lower pressure means a lower saturation temperature. The coil gets too cold, freezing the ambient moisture in the air before it can drain.

• The Fix: Do not let a “handyman” just top off the refrigerant. It is illegal and a waste of money. The leak must be found using an electronic sniffer or dye, repaired, and the system recharged to factory specifications.

3. Evaporator Fan Motor Failure

If the fan motors on the evaporator unit die, the cold air cannot be pushed into the box. The cold stays trapped at the coil, rapidly freezing the ambient moisture.

• The Fix: Fan motors burn out frequently in harsh, freezing environments. They must be replaced with OEM or high-quality universal ECM motors.

4. Poor Box Integrity (Door Left Open)

If the walk-in door is left propped open during a heavy delivery, or if the door gaskets are completely shredded, massive amounts of warm, humid kitchen air will rush into the freezer. This moisture instantly flashes into ice when it hits the freezing evaporator coil, overwhelming the system’s normal defrost capabilities.

What You Should Do Immediately

1. Move Your Product: If the box temperature is climbing above 0°F, start moving high-value inventory to secondary freezers if possible.
2. Force a Manual Defrost: If your controller allows it, force a defrost cycle to see if the heaters engage.
3. Call for Priority Dispatch: Do not attempt to chip the ice off with a screwdriver or knife. You will puncture the aluminum coil, turning a simple repair into a $3,000 evaporator replacement.

If your facility relies on mission-critical refrigeration, contact HP Mechanical for Emergency Repair. Our factory-trained technicians carry the parts required to diagnose defrost failures and repair refrigerant leaks on all major brands, including True, Turbo Air, and Kolpak.

Protect Your Assets: The best way to prevent catastrophic icing is through a Commercial Preventative Maintenance Contract. Routine coil cleaning and system calibration will catch these issues before they take down your kitchen.