A deli owner in Islington sent us a photo of his serve-over display counter. The glass was completely misted up from the inside — customers couldn’t see a thing. He’d been wiping it down every twenty minutes during the lunch rush, but the condensation came back within five. His staff were opening the sliding doors to wipe, which made the problem worse. Sandwiches and salads sitting behind fogged glass don’t sell. He reckoned he was losing 30% of his lunchtime impulse purchases.
Display fridges exist to display product. When the glass mists up, the fridge fails at its primary job. The food is still cold, but nobody’s buying what they can’t see. Here’s what causes it and how to fix it.
Worn or Damaged Door Gaskets — The Most Common Cause
The rubber gaskets around the doors of a display fridge create an airtight seal that keeps warm, humid shop air out of the cold cabinet. When gaskets crack, lose their magnetic grip, tear, or deform from years of use, warm air leaks in continuously. That warm air carries moisture. When the moisture hits the cold glass, it condenses. Misting.
Run your hand slowly around the perimeter of a closed door. If you can feel cold air escaping at any point, the gasket has failed at that section. On multi-door display units, it’s often the most-used door — the one staff open hundreds of times a day for restocking — that goes first.
Gasket replacement is straightforward and relatively inexpensive. We carry common profiles for the major manufacturers. It’s one of the highest-value repairs in commercial refrigeration — a new gasket improves display visibility, reduces energy consumption, and extends the life of the compressor by reducing its workload.
Failed Anti-Sweat Heaters
Most glass-door display fridges have low-wattage heaters embedded in the glass panels or the door frames. These anti-sweat heaters keep the glass surface just warm enough to prevent condensation forming on the outside. On some units, heated glass also prevents internal misting by maintaining a slight temperature differential across the pane.
When these heaters fail, the glass temperature drops to match the cabinet interior, and any humidity in the surrounding air condenses on it. The failure can be partial — one door mists while the others stay clear — or total if the heater circuit has tripped or the controller has failed.
Diagnosing a failed anti-sweat heater requires checking the heater resistance and the controller output. On some units, the heaters run continuously; on energy-efficient models, they’re controlled by a humidity sensor and only activate when condensation risk is high.
Overloading and Blocked Airflow
Display fridges rely on a carefully designed airflow pattern to maintain even temperatures and keep moisture under control. In upright glass-door units, cold air flows from vents at the top or back, circulates across the shelves, and returns to the evaporator at the bottom. Overfilling the shelves or pushing products right up against the back wall and air vents disrupts this airflow.
When circulation stalls, cold spots form near the evaporator while warmer pockets develop near the glass. The temperature differential between the glass surface and the air behind it creates condensation. The solution is disciplined stock loading — follow the load line markers inside the cabinet. They’re there for a reason.
High Ambient Humidity
Some environments are just harder for display fridges. A shop next to an open kitchen, a deli with a constantly boiling bain-marie, a convenience store in a basement with poor ventilation — all generate high ambient humidity that overwhelms the cabinet’s ability to manage condensation.
If the gaskets are fine and the anti-sweat heaters are working but you’re still getting misting, the environment is the problem. Solutions include improving shop ventilation, reducing humidity sources, or upgrading to cabinets with more aggressive anti-condensation systems.
Evaporator Fan Failure
The evaporator fans inside the cabinet circulate cold air and maintain the air curtain effect on open-front displays. When a fan fails, the air curtain collapses and warm shop air floods into the cabinet. On closed-door units, a dead fan creates uneven temperatures and stagnant pockets of moist air that condense on the coldest surfaces — usually the glass.
Listen for the fans when the cabinet is running. If it’s quieter than usual or you can see that one of the fan blades isn’t spinning, that’s your culprit. Fan motors on display cabinets are small, inexpensive, and quick to replace.
Incorrect Temperature Setting
A cabinet set colder than it needs to be creates a bigger temperature gap between the glass and the surrounding air, increasing condensation risk. If the cabinet is set to 0°C but the products only need 5°C, you’re creating unnecessary condensation and wasting energy. Set the temperature to the warmest safe point for your product — typically 2–5°C for most chilled display applications.
Night Blinds on Open-Front Displays
Open-front display cabinets — the multideck units common in convenience stores and supermarkets — rely on an air curtain to separate cold cabinet air from warm shop air. During trading hours, this works reasonably well. Overnight, without the air curtain fans running at full speed, these cabinets are vulnerable to humidity ingress.
Night blinds are pull-down covers that seal the open front of the cabinet outside trading hours. Using them consistently reduces overnight energy consumption by up to 30% and dramatically cuts condensation problems the next morning. If your open-front displays are misting up at the start of each day, check whether night blinds are fitted and whether staff are actually using them.
Display Fridge Misting Up? Call ADK
Misted-up display cabinets cost you sales every hour they’re fogged. We diagnose and fix the root cause — gaskets, heaters, fans, airflow, controls — across all major display fridge brands. Call 020 3974 1419 for a fast response across London.