A display fridge sweats when the air around it is humid enough that the glass, frame or shelving falls below the dew point and moisture condenses out of it. On the Northern Beaches that happens more than most places because coastal air carries more water. Sometimes the cabinet is doing exactly what it should in a humid room. Often it is telling you that a heater, a seal or the airflow around it has failed.
Why condensation forms at all
Every commercial cabinet is fighting the same physics as a cold drink on a summer afternoon. If a surface is colder than the dew point of the air touching it, water condenses on it. Manufacturers deal with this in two ways: by keeping outside surfaces slightly warm with low-power heaters in the door frames and glass, and by keeping the humid air out with seals and, on open-front cabinets, an air curtain.
When condensation appears where it did not before, either the air has become more humid, or one of those defences has stopped working, or the cabinet is running colder than it was designed to.
Reading where the water is
| Where the moisture is | Most likely cause |
|---|---|
| Outside of the glass doors, wiping clear | Humid room air, or the door heater circuit has failed |
| Frame between two doors, or around the door edge | Frame heater failed, or the seal is no longer sitting flat |
| Inside the cabinet, on shelves and product | Warm humid air getting in: seal, hinge, a door left ajar or too many openings |
| Pooling at the bottom or dripping underneath | Blocked drain or evaporator drip tray, often with ice on the coil |
| Only on hot, humid days | The room rather than the cabinet: ventilation, and where the cabinet sits |
The door heater nobody knows is there
Most glass-door cabinets have a heating element running through the door frame and sometimes the glass itself. It draws very little power and its only job is to keep the outside surface above the dew point. When it fails, the doors sweat on any humid day, and because nothing else changes, the fault is usually blamed on the weather. If a cabinet that never sweated has started to, and the seals look fine, the heater circuit is the first thing to check.
Open-front cabinets and the air curtain
An open display case keeps its cold in with a curtain of moving air flowing down across the front. That curtain is fragile. A ceiling fan, an air-conditioning vent, a door that opens onto it or even a busy aisle will push warm humid air past it and into the cabinet, where it condenses and warms the front shelves. If an open cabinet sweats or runs warm at the front, look at what is moving the air around it before looking at the refrigeration.
Night blinds make a large difference on open cabinets, both to condensation and to running cost, and are worth using whenever a cabinet is not being shopped.
The coastal factor
Beachfront venues on the Northern Beaches see higher humidity than inland ones, and cabinets that would be fine in Frenchs Forest can sweat persistently in Manly or Newport. That does not mean the cabinet is faulty, but it does mean the defences have to be in good order: heaters working, seals sound, drains clear. It also means positioning matters. A cabinet by an open door to the street will always struggle more than one set back inside.
What to check before calling
- Close the door on a strip of paper: if it pulls out easily, the seal is not sealing
- Feel the door frame: it should be faintly warm to the touch, not cold
- Look for ice on the evaporator or water in the drip tray
- Note whether the sweating tracks with the weather or is constant
- Check what is blowing air across the front of an open cabinet
If the seals and airflow are sound and the frame is cold, the heater circuit or a control has failed and the cabinet needs looking at. If the cabinet is icing up as well as sweating, the defrost has probably stopped working, and that is worth fixing quickly.