Walk-In Cooler Smells Bad or Has Mold? Find the Source

A walk-in cooler shouldn't have a smell beyond whatever product is in it. A sour, musty or rotten odor means something is growing or decaying, and in a closed, humid box it spreads to everything, including product. Mold that keeps coming back usually means water is collecting somewhere you can't see.

The fix starts with finding the source. Cleaning the walls won't help if the smell is coming from the drain pan.

Where walk-in odors come from

Spilled and spoiled product

The most common source is the simplest: a leaking container, broken egg, dripping meat package or forgotten produce, often under the bottom shelf or behind cases against the wall. Cold slows decay but doesn't stop it.

The drain pan and drain line

The evaporator collects water every time it defrosts. That water runs into a drain pan under the coil and out through a drain line. If the pan doesn't drain completely, or the line is partly clogged, water sits in the pan and grows slime and mold. The smell gets blown around the box by the evaporator fans. A slow drain also causes water on the floor and water spitting from the evaporator.

Heatcraft's unit cooler manual calls for drain lines pitched at least ¼ inch per foot, trapped, and run to an open drain rather than directly into a sewer. A line that's sagging, untrapped or tied directly into the sewer can let sewer gas back into the box. On freezers the drain line also needs a heater; see drain line heater.

The evaporator coil

The coil's fins are cold and wet, and they catch whatever is in the air: food particles, dust, cardboard fibers. Over time a film builds up that can smell and grow mold. It also cuts airflow. Coil cleaning is part of Heatcraft's recommended maintenance at least every six months, along with the drain pan and drain line. See evaporator coil.

Humidity

Coolers run at high humidity by design. Heatcraft's engineering manual says a general-purpose cooler balanced at a 10°F to 12°F coil temperature difference runs about 80% to 85% relative humidity, and produce rooms balanced at 7°F to 9°F run about 90%. That's good for product and good for mold. It's why regular cleaning matters more in a walk-in than in a dry storeroom.

Wet insulation: when the panels are the source

If you've cleaned everything and a musty smell stays, the source may be inside the walls, ceiling or floor. Walk-in panels are foam insulation sandwiched between metal skins. Water can get in through damaged skins, open seams, failed caulk or roof leaks on outdoor boxes. Once the foam is wet, it holds water, loses insulating value and can grow mold where you can't reach it.

Signs of wet insulation include:

• a smell with no visible source that returns after cleaning;
• panels that feel soft, bulge or have rust stains at seams;
• a spot on an inside wall that frosts or stays wet;
• a spot on the outside that sweats when nearby panels don't.

See panels and insulation and walk-in floor. Our post on polystyrene vs polyurethane insulation explains how panel types differ.

Checks staff can do safely

1. Empty and inspect. Move product out one section at a time, keeping it cold. Look under and behind shelving, along wall bases and in corners.
2. Toss what's spoiled following your normal waste and discard procedure.
3. Get rid of damp cardboard. Replace soft or wet boxes with clean containers where you can.
4. Clean and sanitize surfaces. Use a food-safe detergent, rinse, then a sanitizer approved for food-contact areas at the label strength. Dry what you can. The cleaning a walk-in cooler page covers the full process.
5. Clean gaskets and strip curtains. Wipe gasket folds with mild detergent and warm water and dry them. Don't use sharp tools.
6. Look at the evaporator from the floor. Is water dripping? Is there dark buildup on the coil face you can see? Is the drain pan overflowing? Report it; don't open the evaporator.
7. Check the floor. Look for soft spots, cracks holding water, or water under the door threshold.
8. Keep notes. If the smell returns, note where and how soon. That points the technician to the source.

Safety: Don't spray water or cleaner into the evaporator fans, electrical fittings, light fixtures or the controller. Turn the evaporator off at its disconnect before cleaning close to it, and confirm the fans have stopped. Drain pan and coil cleaning are technician tasks.

Food safety: Don't store food on the floor, and keep cleaning chemicals out of the walk-in. If mold or spoilage may have reached product, your local health authority's rules govern what can be kept.

What a technician will check

• Open the evaporator's access panel, clean the drain pan and flush the drain line.
• Check drain line pitch, trap, heater (freezers) and where it discharges.
• Clean the evaporator coil with a cleaner suited to the coil material.
• Look for condensation from a failing door heater or insulation gap.
• Check panel seams, skins and the floor for water intrusion, and test suspect panels.

When it points to replacement

Most odor problems end with cleaning and a drain repair. The exception is waterlogged panels or floors. Wet foam doesn't dry out in place, and panels that are soaked, delaminated or rotting usually need to be replaced. That can be a section or the whole box depending on age and extent. JayComp supplies and installs replacement panels and complete walk-ins from manufacturers including Leer and KPS if you reach that point. The lifespan page covers how panels age.