Walk-In Cooler Not Cooling: Causes, Safe Checks and When to Call

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A walk-in cooler that is running but not getting cold usually has one of a short list of problems: warm air getting in, air not moving across the evaporator coil, heat not getting out at the condenser, or a refrigeration fault inside the sealed system. This page walks a manager through the symptoms in that order, shows what staff can safely check in the first few minutes, and marks the point where you stop and call a technician. It is part of our Commercial Refrigeration Help Center.

Start with two numbers: the box and the product

The thermometer on the wall reads air, and air swings every time the door opens. Product temperature tells you how serious the problem is. CalCode requires a thermometer in each refrigeration unit, placed to read the warmest part of the unit (HSC 114157), so compare that reading with a probe reading from a case of milk or a tray of prepped protein near the door. If the product is still at 41°F or below, you have time. If the product is climbing, move the most sensitive items to another cooler while you troubleshoot. Our food safety page covers what the California Department of Public Health says to keep and what to discard.

Symptom table: what you see and what it usually means

What staff can safely check

1. Power and settings. Look at the controller or thermostat. Is the display on, is the set point where it should be, and does it show a defrost or alarm code? Check the breaker for the condensing unit and the evaporator, and the disconnect switch by the unit. Reset a tripped breaker once only.
2. The door. Close it and look for light around the edges. A torn or flattened gasket, a door that no longer closes on its own, or a strip curtain that has been tied back lets warm, humid kitchen air pour in. Norlake warns that leaving a walk-in door open for more than five minutes can form a film of ice or moisture on the floor, ceiling and walls, and recommends vinyl strip curtains to cut the warm air coming in (Norlake walk-in manual).
3. Airflow inside the box. Product stacked tight against the evaporator, or cases on the floor under it, starve the coil of air. Leave clear space in front of the fans and between shelves and walls.
4. The evaporator coil. With a flashlight, look at the coil fins behind the fan guard. A light, even frost that clears during defrost is normal. A white block of ice is not. Do not chip at it with a knife or scraper; the tubes are thin and puncturing one turns a service call into a refrigerant leak.
5. The condenser. On a rooftop or outdoor unit, clear cardboard, leaves and trash from around it. On an indoor unit, make sure nobody has stored boxes against it or closed off the room it breathes from. Do not open the unit panels or hose the coil while it is powered.
6. Write it down. Times, box and product temperatures, what you checked and what changed. A technician will ask for exactly this.

Stop and call when you see any of these

• A breaker that trips a second time, a burning smell, buzzing from the electrical box, or scorched wiring.
• An evaporator coil encased in ice, or water spitting from the fans.
• The condensing unit running constantly with a clean coil, or starting and stopping every few minutes.
• Any sign of a refrigerant leak: hissing, oil stains on fittings, or frost on one spot of a line.
• Product temperatures still rising after the quick checks.

Staff should not open the refrigerant circuit, add refrigerant or adjust valves. Federal rules require anyone who could open a refrigerant circuit to be EPA Section 608 certified (40 CFR 82.161). Never jump out a pressure switch or other safety control to keep a compressor running; those controls are there to stop it from destroying itself.

The common causes, in more detail

Ice on the evaporator coil

This is the most common reason a walk-in runs but stays warm. Turbo Air's walk-in systems manual lists the symptoms of ice forming in a coil as loss of air circulation and air throw, loss of room temperature, no off-cycle time, flood back, and water spitting from the fans or coil on air defrost systems, and warns that long-term ice will crush the refrigerant tubes and cause leaks (Turbo Air manual). The usual root causes are a defrost heater, timer or defrost termination control that has failed, a plugged drain, or too much humid air coming in through the door. Our walk-in freezer ice buildup page covers the defrost side in detail.

Fan motors

If one evaporator fan has stopped, the coil ices faster and the box develops warm spots. A fan that is noisy, slow or stalled needs replacing. Current federal walk-in standards require evaporator fan motors under 1 horsepower to be electronically commutated (EC) or three-phase motors (10 CFR 431.306), so a replacement is normally an EC motor.

A dirty or starved condenser

The condenser throws the heat from the box outdoors. When the coil is matted with grease and dust, or the unit sits in a hot, closed space, head pressure rises and cooling capacity falls. Turbo Air's troubleshooting chart pairs high discharge pressure with a dirty condenser coil (Turbo Air manual), and Heatcraft's condensing unit manual calls for checking the condenser quarterly and cleaning the coil and fan blades semi-annually, with no acid-based foam cleaner (Heatcraft manual).

The door and door heater

Kolpak's manual says frost or condensation around the door jamb or heated pressure relief vent means the heater is not working or there is too much moisture, and that the gasket should seal around the entire door perimeter (Kolpak manual). Federal walk-in standards also require automatic door closers on most walk-in doors and strip doors or another way to limit infiltration when the door is open (10 CFR 431.306).

Refrigerant, TXV and controls

Turbo Air's chart lists insufficient refrigerant, superheat too high, a room thermostat set too high and an iced coil as causes of insufficient cooling, and lists lack of refrigerant, a dirty or iced evaporator and a clogged liquid line filter drier as causes of low suction pressure (Turbo Air manual). A system that is low on refrigerant has a leak, and topping it off without finding the leak only buys time. Our guide to refrigerant leak causes and symptoms explains why.

How a technician diagnoses a warm walk-in

We start where you did: box and product temperatures, controller settings and alarm history. Then we measure. Suction and discharge pressures, superheat at the evaporator and subcooling at the condenser tell us whether the system is low on refrigerant, overcharged, restricted, or fighting a dirty condenser. We check fan motor amps, the defrost heater and its termination control, the drain line and its heater, the contactor and the compressor. If the coil is iced, we defrost it properly before judging anything else, because an iced coil makes every other reading misleading. Our refrigeration technicians advise managers to write down what the display showed and what they already reset before we arrive.

For a sense of what these repairs involve and cost, read our walk-in cooler repair cost guide. If your cooler shows the slow warning signs rather than a sudden failure, see signs your walk-in cooler is failing. When a downtown San Jose Taco Bell walk-in failed at peak hours, the repair we made kept the restaurant from losing its food.

Preventing the next warm box

• Keep the door closed and the closer, gasket and strip curtain in working order. Norlake recommends quarterly preventive maintenance by a certified technician, including gasket checks, door sweep adjustment, heated vent port inspection and cleaning the evaporator and condenser coils (Norlake walk-in manual).
• Log box temperatures every shift so a slow drift shows up before it becomes a loss.
• Book routine service through our walk-in cooler repair and service team, which carries our 1-year parts and labor warranty on every job.

Schedule a walk-in cooler repair

Frequently asked questions

Written and reviewed by Jim McKinny, owner of Cool Aid Air Conditioning & Refrigeration — California C-20 and C-38 licensed, EPA Universal certified, second generation of a family business serving the Bay Area since 1966. Every job we complete is backed by our 1-year parts & labor warranty.