Walk-In Cooler Making Noise? A Sound-by-Sound Guide

A new noise is often the first warning a walk-in gives before a failure. Fan bearings grind for days or weeks before they seize, and a compressor that knocks is telling you something is wrong with what's coming back to it. Catching the sound early can mean replacing a part instead of losing a load of product.

Walk-ins have two noise sources: the evaporator inside the box (fans, coil, defrost heaters, drain) and the condensing unit outside or on the roof (compressor, condenser fan, electrical controls). The first step is working out which one the sound comes from.

Sound-by-sound guide

Squealing, whining or grinding: fan motors

Both the evaporator and the condenser use fan motors. When the bearings wear, the motor squeals at start-up, then whines or grinds steadily. The sound usually gets worse over time, and the motor may start running slowly or stop, which leads to an iced coil (evaporator side) or high head pressure (condenser side).

• Inside the box: see evaporator fan motor.
• On the condensing unit: see condenser fan motor.

Rattling from the evaporator: ice on the fan

A rhythmic ticking or scraping from the evaporator often means a fan blade is hitting ice that has built up around the fan shroud or on the coil. That's a defrost or drain problem showing itself. The ice keeps growing until the blade stalls or breaks. See evaporator coil frozen for the safe way to deal with it. Never chip ice away from a fan.

Clicking: contactors and relays

A single solid click when the compressor starts and stops is the contactor, the heavy switch that powers the compressor. That's normal. Clicking every few seconds or minutes is not. It can mean the compressor is short cycling, a safety control is tripping and resetting, or a start relay is failing. A contactor that buzzes or chatters may have worn contacts or be getting low control voltage.

Humming without starting

If you hear the compressor hum for a few seconds, then a click, and nothing starts, the compressor is trying to start and can't. Common causes are a failed start or run capacitor, a bad start relay, low supply voltage, or a compressor that's mechanically stuck. The internal overload then trips and the cycle repeats. Each failed start is hard on the motor and wiring, so this needs a technician the same day. See compressor not running and contactor, capacitor and relay.

Knocking or banging from the compressor

A compressor is built to pump vapor, not liquid. If liquid refrigerant returns to it, you can hear knocking or banging. Heatcraft's condensing unit manual warns that low superheat "promotes liquid slugging and compressor bearing washout." Frost on the suction line or the compressor body often goes with it; see frost on the suction line. Knocking can also mean internal mechanical wear. Either way it's serious. Call a technician and describe the sound.

Hissing and gurgling

Refrigerant flowing through the expansion valve and lines can make a soft hiss or gurgle, especially right after the compressor starts. That's usually normal. Be concerned if:

• the hiss is new and steady, from one spot, especially at a fitting or valve;
• you see oily residue near the sound;
• the box is also losing its ability to hold temperature.

Those point to a leak. Walk-ins are enclosed spaces, and EPA notes refrigerant can cause asphyxiation if vapor displaces air in a confined space. See refrigerant leak safety.

Popping and creaking panels

Panels and their metal skins expand and contract as the box cools down, warms during defrost, or as door openings change the pressure inside. Occasional pops are common. In freezers, loud creaking or panels that visibly flex when the door closes can mean the pressure relief port is iced or blocked. The door is usually hard to open at the same time; see freezer door hard to open.

Checks staff can do safely

1. Locate the sound. Inside the box near the evaporator, or outside at the condensing unit? Near the fans, or the compressor?
2. Note the timing. Constant? Only at start-up? Every few minutes? Only during or after defrost?
3. Record it. A 30-second phone video with sound, plus the controller display, helps the technician more than a description.
4. Look, don't touch. Check whether the evaporator fans are all turning, whether there's ice on the coil face or fan guards, and whether anything is lying on or against the condensing unit.
5. Clear debris outside. With nothing running near your hands, remove loose boxes, bags or leaves that are resting against the outside of the condensing unit. Don't open panels.
6. Check the box temperature. A noise plus a rising temperature is more urgent than a noise alone.
7. Pass the details on. The what to tell your technician checklist covers what else to note.

Safety: Evaporator fans stop during defrost and can restart automatically, sometimes after a delay. Never reach into a fan guard or put tools near a fan, even when it's not moving. Condensing unit fans also start without warning.

What a technician will check

• Fan motors for bearing noise, speed and current draw; blades for damage or ice contact.
• Contactor contacts, start and run capacitors, start relays and control voltage.
• Compressor amperage, mounting and internal condition.
• Superheat at the evaporator and compressor, to rule out liquid returning.
• Defrost operation if ice is involved.
• Leak checks if a hiss or oil residue is present.

When it points to replacement

Most noises are fixed with a fan motor, a capacitor or relay, or a contactor. A compressor that knocks from internal wear is a bigger decision, especially on an older system. The compressor page and repair or replace guide cover when a new compressor or condensing unit makes more sense. For Heatcraft-specific steps, see Heatcraft walk-in troubleshooting.