Walk-In Cooler Too Cold and Freezing Product? Find the Cause

A cooler that's too cold gets less attention than one that's too warm, but frozen produce, dairy and beverages are real losses, and the cause is often a part that's about to fail in a worse way. A welded contactor, for example, keeps the compressor running with no way to stop it.

Start by working out which of two problems you have: the whole box is too cold, or only some product is freezing.

Whole box cold, or just some product?

Only certain product is freezing. If the box reads normal but items on one shelf freeze, the cause is almost always air pattern. The evaporator (the fan-coil unit hanging near the ceiling) blows air well below box temperature out of its face. Product stacked directly in that stream, or pushed against the coil, freezes even when the rest of the box is fine. See stocking and airflow.

The whole box is cold. If a separate thermometer shows the box air well below the setpoint, the system is either being told to cool too much or can't stop. That's a controls or electrical problem.

What's usually behind it

Setpoint and controller

A common walk-in setup is an electronic controller on the evaporator reading a room probe. Heatcraft ships its air-defrost cooler controls with a 35°F default setpoint. If your box reads 28°F, the first thing to confirm is what the controller is set to, then what it's reading. The thermostat and temperature controller page covers mechanical thermostats versus electronic controllers and how to read the setpoint.

Probe problems

The controller only knows what its probe tells it. If the probe has been knocked loose and is hanging against a warm surface, or near the door where warm air comes in, the controller thinks the box is warmer than it is and keeps cooling.

A failed probe can also cause over-cooling on some controllers. On a Dixell XR60CX, for example, a room probe failure (shown as P1) makes the compressor run on a fixed on/off pattern set by the Con and COF parameters instead of by temperature. If those are set aggressively, the box can drift cold. Other brands show probe errors differently; the controller alarm codes page lists verified codes by brand.

Stuck solenoid or welded contactor

Many walk-ins use a pump-down control: the controller opens and closes a liquid line solenoid valve, and the compressor stops when suction pressure drops. If the solenoid sticks open, refrigerant keeps flowing and the compressor keeps running after the box is cold. See liquid line solenoid valve.

The contactor is the heavy-duty switch that powers the compressor. Its contacts can weld together from arcing, so the compressor runs no matter what the controller says. The contactor, capacitor and relay page explains why this is tech-only work: contactors carry line voltage.

Both failures also make the box run constantly, and a compressor that can't stop is at risk of other damage.

Checks staff can do safely

1. Confirm with a separate thermometer. Put a trusted thermometer in the middle of the box, away from the evaporator discharge and the door, for several minutes. The FDA Food Code requires ambient air thermometers to be accurate to ±3°F. Compare it to the controller display.
2. Check the setpoint. Using the controller manual, read the setpoint. If it's clearly wrong (for example, set to a freezer value), note what it was before you change anything, and have a manager correct it.
3. Look at the controller display for a code. Low-temperature alarms show as LA on Dixell, LO on Carel ir33, A2 on Heatcraft Beacon II, BOXLO on the Heatcraft Smart Controller and AL02 on Heatcraft intelliGen. Write down any code.
4. Find the room probe. It's usually a small sensor on a wire near the evaporator's air inlet. If it has fallen, is taped to a wall near the door or is buried in product, tell the technician. Don't cut or unplug it.
5. Move product out of the evaporator airflow. Keep cases off the face of the evaporator and out of the stream of air it blows.
6. Listen to the condensing unit. If the box is well below setpoint and the compressor never stops, tell the technician that when you call. It points to the solenoid or contactor.
7. Check your thermometer. A food thermometer can be checked in a cup of ice water. It should read 32°F. If it doesn't, adjust or replace it before trusting its readings.

Tip: Don't turn the controller off to stop over-cooling unless a technician tells you to. If a contactor is welded, switching the controller off may not stop the compressor, and you lose the display and alarm history.

What a technician will check

• Controller calibration against a reference thermometer. On Heatcraft intelliGen controls, the manual gives a probe resistance check at 32°F in ice water, and a probe well outside it gets replaced.
• Probe position and wiring, including whether it's in the right spot for the box's airflow.
• Controller parameters such as setpoint, differential and any fallback settings after probe failure.
• Liquid line solenoid: whether it closes when de-energized, and whether the coil is getting voltage when it shouldn't be.
• Contactor: whether the contacts open when the coil is de-energized.
• Pump-down pressure control settings, since a low-pressure control set wrong can keep the compressor running.
• Evaporator airflow and whether product placement is causing local freezing.

These are straightforward parts repairs. A too-cold cooler rarely points to replacing the system.

Special cases

• Eggs and produce. Raw shell eggs must be stored at an ambient air temperature of 45°F or less under the Food Code. Many products, like leafy greens, are damaged near freezing, so they need spots away from the coil.
• A cooler that swings cold then warm is a different pattern. See temperature fluctuating.
• Beverages in a beer cave can freeze and burst in the coldest spots. Keep them out of the evaporator discharge.

For how the pieces of the system work together, see how walk-in coolers work. For controller-specific steps, see Heatcraft controller troubleshooting.