What do the alarm codes on my walk-in cooler mean?

Here's the thing that trips people up when a walk-in starts alarming: the brand on the door — Norlake, Kolpak, or a local box builder — usually isn't the brand doing the talking. The box is insulation and panels. The alarms come from the refrigeration system and its controller, and a handful of controller families cover most of the commercial market. Identify which one you're looking at and go straight to its full code list — then use the second half of this page to understand what the controller is actually measuring.

Which controller is talking?

Heatcraft intelliGen — AL, ER and IN codes

Heatcraft (whose equipment sells under the Bohn and Larkin names) ships the intelliGen controller on current unit coolers: a small OLED display with a colored light bar. Red bar plus an AL code is an alarm — AL01 is high box temperature, AL06 the door. Yellow plus an ER code is an error, usually a sensor. IN codes are information. Units on A2L refrigerants add leak-detection codes (AL12, ER32–ER37) that you treat as evacuate-and-call events. Every intelliGen code →

Heatcraft Beacon II — A and E codes

The previous generation shows A1–A4 alarms and E1–E9 errors on the evaporator board's LED readout, with an optional Smart Controller LCD that shows text like *BOXHI and +COMM+. Several of its faults pump the system down and keep it off until the failed part is replaced, which makes them urgent. Every Beacon II code →

KE2 Therm — named, scrolling alarms

KE2 Evaporator Efficiency controllers don't use cryptic codes at all — they scroll names: HIGH AIR TEMP, DOOR SWITCH, EXCESS DEFROST, LOW SUPERHEAT. A yellow LED means the system is still running; a red-LED alarm like PRESSURE SENSOR means it shut down to protect the compressor, and the clock is running on your product. Every KE2 alarm →

Dixell — the two-letter codes on Norlake, Kolpak and many others

The little Dixell (Emerson) XR-series thermostat is everywhere in walk-ins. Its codes are terse: P1–P4 are probe failures, HA/LA high and low temperature alarms, dA the door, EA/CA external alarms — with CA being the serious one that switches everything off. The one that generates the most confused phone calls isn't a fault at all: OF/PoF just means the keypad is locked. Every Dixell code →

Carel — ir33 and PJ Easy

Carel's compact controllers flash short codes that alternate with the temperature: E-codes for probes, HI/LO for temperature, dor (ir33) or dOr (PJ Easy) for the door, and a condenser pair where lowercase cht is the early warning and uppercase CHt the hard alarm. Every ir33 / ir33+ code → · Every PJ Easy code →

Danfoss — ERC, EKC / AK-CC and Optyma Plus

Danfoss uses E-codes for sensor and controller faults and A-codes for alarms; the EKC 202 and AK-CC 210 add S-codes that explain why the box isn't cooling right now, and the Optyma Plus controller on the condensing unit reports pressure and discharge-temperature protections. ERC 211/213/214 → · EKC 202 / AK-CC 210 → · Optyma Plus →

Norlake control panels — plain-text alarms

Norlake's programmable walk-in panels (built on Carel hardware) skip codes entirely and scroll plain text: DOOR AJAR ALARM, ROOM TEMP HIGH ALARM, AIR FLOW LOSS. Read them literally, silence with the ALARM button while you investigate, and check the status line for fallback modes like SENSOR FAIL MODE that mean the panel is running on backup logic. All 22 Norlake alarms →

What is the controller actually watching?

Every walk-in runs the same loop. Inside the box, the evaporator — the unit cooler with the fans — is where liquid refrigerant boils and soaks up the box's heat. The compressor pulls that vapor away and squeezes it to a high pressure. Outside, the condenser dumps the heat into the outdoor air and turns the refrigerant back into liquid. An expansion valve meters that liquid back into the evaporator, and the loop starts again. A controller doesn't see any of this directly. It sees temperatures and, on the smarter systems, pressures — and every alarm code on this site is one of those readings crossing a line.

How does a controller hold temperature?

A controller cycles the system around a setpoint with a differential. Heatcraft's intelliGen, for example, calls for cooling when box temperature rises above the setpoint plus half the differential, and ends the cycle when it falls below the setpoint minus half the differential: it closes the expansion valve, pumps the refrigerant out of the evaporator, and the compressor stops when suction pressure drops below the low-pressure switch's cut-out. Minimum run and minimum off times keep the compressor from short-cycling. Temperature alarms are deliberately slow — controllers wait out an alarm delay before raising a high-temperature alarm, so a door propped open for a delivery doesn't page anyone.

The temperature sensors are thermistors: their resistance changes with temperature, which is how you test them. The curves differ by manufacturer. A Heatcraft sensor reads 10,000 Ω at 77 °F and 32,650 Ω at 32 °F; a KE2 sensor reads about 2,000 Ω at 77 °F and 5,114 Ω at 32 °F. Sensors aren't interchangeable between brands, and controllers that accept several sensor types have to be set for the one fitted.

What is superheat — and why do controllers alarm on it?

Superheat is how many degrees the refrigerant vapor leaving the evaporator is above the temperature it boiled at. Controllers with an electronic expansion valve work it out from a suction pressure transducer and a suction temperature sensor, then open or close the valve to hold a target. Beacon II's factory default is 7 °F at the evaporator, adjustable so the compressor sees 20–30 °F.

Too little superheat means liquid refrigerant can reach the compressor, which is why intelliGen (ER16), Beacon II (E6) and KE2 (LOW SUPERHEAT) all flag it. KE2 points out that the most common real cause is simpler: the compressor never started, often because a low-pressure control was never set in the field. Too much superheat means the evaporator is starved of refrigerant — KE2's HIGH SUPERHEAT alarm fires when superheat stays above setpoint with the valve nearly wide open, and a short refrigerant charge is one cause.

What is subcooling?

Subcooling is the mirror image on the high side: how far the liquid leaving the condenser has been cooled below its condensing temperature. Subcooled liquid stays liquid all the way to the expansion valve; without enough of it, refrigerant can "flash" into vapor in the liquid line, which Heatcraft notes causes extra pressure drop and poor expansion-valve operation. None of the controllers on this site alarm on subcooling directly — it's a gauge-and-thermometer reading a technician takes. It's also one reason "just add refrigerant" is the wrong reflex: Heatcraft reminds installers that bubbles in a sight glass can mean a restriction as well as a shortage.

Why do walk-ins defrost — and what goes wrong?

Moisture in the box freezes onto the evaporator coil, and frost blocks the airflow, so controllers defrost on a schedule or on demand. Coolers typically use air (off-cycle) defrost: refrigeration stops and the fans keep running until the frost is gone. Freezers use electric defrost: the fans stop and heaters in the coil switch on until the coil sensor reaches its termination temperature, with a fail-safe time as the backstop. After an electric defrost comes a drain-down period, then a refreeze, when the fans stay off until the coil is cold again.

Controllers flag defrosts that go wrong. Carel's Ed/Ed1 and KE2's DEFR TERM ON TIME mean a defrost ended on the timer instead of temperature; intelliGen's IN01 and IN05 flag runs of too-short defrosts or of defrosts that timed out; a failed coil probe forces every defrost onto the timer (Dixell P2). The meltwater has to go somewhere, too. Heatcraft specifies drain lines pitched at least ¼ inch per foot, traps on freezers outside the refrigerated space, and heat tape plus insulation wherever a line or trap could freeze. Its troubleshooting table lists the usual causes of ice in the drain pan: a defective heater, a unit not pitched properly, a plugged drain line, a defective drain-line heater, or a faulty timer or thermostat. More in the ice buildup guide.

Why does the condenser matter so much?

All the heat the evaporator picks up has to leave through the condenser. A dirty coil, a failed fan or boxes stacked against the unit push condensing temperature and pressure up until a safety trips — which is why so many controllers watch it: Carel's cht (early warning) and CHt (hard alarm), Dixell's HA2, Danfoss's A61 and A80. On the Optyma Plus, Danfoss's whole instruction for A80 is "clean the condensing unit." Heatcraft's list of high-pressure trip causes is the complete picture: overcharge, non-condensables, the condenser fan motor or blade, a dirty condenser coil, head-pressure or fan-cycling controls, and liquid-line restrictions.

The compressor sits between the two, protected by the pressure switches and overloads these codes report. General compressor theory — how compressors work and why they fail — is covered on our sister site aircompressorcodes.com; this site stays with what walk-in controllers report.

Which refrigerants — and why does the controller need to know?

Heatcraft's intelliGen manual carries tables for R-404A/R-507, R-407A, R-407C, R-407F, R-448A and R-449A, plus the A2L (mildly flammable) refrigerants R-454A, R-454C and R-455A used on newer equipment. The controller turns suction pressure into a boiling temperature using its refrigerant setting, so a wrong setting corrupts every superheat calculation — Heatcraft's troubleshooting sequences include "check refrigerant type," intelliGen has a refrigerant-mismatch code for A2L units (ER36), and the Optyma Plus raises A11 when no refrigerant has been selected. A2L unit coolers also carry a refrigerant detection system; when it senses a leak at the mitigation level it takes over and intelliGen shows AL12.

Commercial ice machines run this same vapor-compression cycle plus a harvest stage that releases the ice; for ice-making specifics, see our sister site icemachinecodes.com.

The universal rules, whatever the controller

1. Photograph the display before resetting anything. The code plus the box temperature is your service call in one picture.
2. Know whether the system is still running. A running system with a high-temp alarm is urgency measured in hours; a shut-down system is urgency measured in product.
3. Log box temperature every 30 minutes during any event — for food safety compliance and for your own diagnosis.
4. One reset is diagnosis. An alarm that returns is telling the truth; forcing restarts against a pressure or superheat fault is how compressors die.

When the code points past what staff can safely do, the verified service lists for Nashville and Birmingham cover contractors who work on all of these systems.