What do Norlake programmable walk-in controller alarms mean?
Short answer: Norlake's programmable panel spells alarms out in plain English. The ALARM button glows red and a buzzer sounds; press ALARM once to silence the buzzer, press it again to see the first alarm screen, and keep pressing to step through each active alarm until "NO MORE ALARMS". Each screen shows the date and time, and some carry a hint — for example "AIR FLOW LOSS 1 — Check Blower, Belts".
Which machines use it?
This is Norlake's programmable walk-in controller — a control panel built on the Carel PCO5+ platform, supplied with Norlake walk-in coolers and freezers and their refrigeration packages. Unlike the tiny code-flashing thermostats on many boxes, this one has a multi-line LCD that spells alarms out in full English — DOOR AJAR ALARM, ROOM TEMP HIGH ALARM, AIR FLOW LOSS — with an ALARM button that silences the buzzer and steps through active alarms. The status line on MENU 1 also tells you when the controller is running on a backup sensor. Practical tip: pressing ALARM after closing a left-open door doesn't just silence the noise — it deliberately delays the air-temperature alarm to give the room time to recover, which is exactly what Norlake intends you to do.
How do you read and clear the display?
Read the status line on MENU 1 too: USING PROD SENSOR means the air temperature sensor has failed and the room is being held on the product sensor; SENSOR FAIL MODE means the air and product sensors have all failed and — if sensor-fail control is enabled — the unit is running on the fixed Cool On / Heat On times. Cooling continues in both cases, but on backup logic.
How do you enter the parameter menu?
The Norlake panel has a 4-line, 20-character display, a row of labelled polycarbonate keys — MENU, SET, PROG, AUX1, AUX2, CLOCK, I/O and MAINT — and five square buttons: on/off, alarm, Up arrow, Down arrow and Enter. From the operation manual:
- alarm shows the active alarms, resets them manually and silences the buzzer; its red LED means at least one alarm has occurred.
- Up / Down arrows move through the screens and raise or lower a value when the cursor is in a field.
- Enter moves the cursor between fields and confirms what you typed.
- MENU opens display-only screens — MENU 1 status and temperatures, MENU 2 system demands, MENU 3 current set points. Nothing can be changed here; step through them with the Down arrow.
- SET opens the set-point screens (room temperature, schedule, alarm limits).
- PROG opens configuration: press PROG, press Enter to move to the field you want, then the Down arrow to enter that setup function. The Technician Menu under it (Config Setup, Control Setup, Lighting Setup) holds the delays behind the alarm table — System Delay, Door Al Delay and Comp Al Delay are on the System Setup 1 screen.
Passwords: there are two levels. Level 1 allows editing set points; level 2 allows editing configuration. A new panel has no password protection at all — the passwords are set in the PARAMETERS group — and Norlake recommends using them, because factory settings changed by accident are "very dangerous" in its own words. When one is set, an ENTER PASSWORD screen appears: press Enter to move to the four digits, Up/Down to change them, Enter to submit. WRONG PASSWORD lets you retry; MENU returns to the System Status screen.
Every Norlake programmable controller code at a glance
| Code | What it means |
|---|---|
| DOOR AJAR ALARM | Door open too long |
| ROOM TEMP HIGH ALARM | Room air temperature above high limit |
| ROOM TEMP LOW ALARM | Room air temperature below low limit |
| ROOM TEMPERATURE SENSOR FAILURE | Air temperature sensor failed |
| AIR FLOW LOSS 1 | Evaporator air flow lost |
| POWER RESTART | Power was interrupted |
| EEPROM FAILURE | Controller memory (EEPROM) failure |
| AIR FLOW LOSS 2 | Air-flow alarm from the second air-flow input (AIRFL2) |
| PRODUCT TEMPERATURE HIGH ALARM | Product temperature above the product high set point for longer than the alarm delay |
| PRODUCT TEMPERATURE LOW ALARM | Product temperature below the product low set point for longer than the alarm delay |
| ROOM HUMIDITY HIGH ALARM | Room relative humidity above the high RH set point for longer than the delay (humidity-controlled rooms) |
| ROOM HUMIDITY LOW ALARM | Room relative humidity below the low RH set point for longer than the delay |
| COMPRESSOR 1 HIGH/LOW PRESSURE | Compressor 1 alarm input (C1 AL) is active — a high- or low-pressure safety has tripped |
| COMPRESSOR 2 HIGH/LOW PRESSURE | Compressor 2 alarm input (C2 AL) is active |
| HI-LIMIT HUMIDISTAT WATCH PERSONAL SAFETY | High-limit humidistat alarm from the humidity alarm input (HUM AL); the alarm text itself carries a personal-safety warning |
| DRAIN PAN ALARM | Drain alarm input (DRAIN) is active — PCO Medium controllers only |
| WATER ALARM | Water alarm input is active |
| SMOKE DETECTION SYSTEM OFF | Smoke alarm input (SMOKE) is active — PCO Medium controllers only |
| PRODUCT TEMPERATURE SENSOR ALARM | Product temperature sensor failure |
| PRODUCT 2 TEMPERATURE LOW ALARM | Second product sensor below its low set point (rooms with two product sensors) |
| PRODUCT 2 TEMPERATURE HIGH ALARM | Second product sensor above its high set point |
| PRODUCT 2 TEMPERATURE SENSOR FAILURE | Second product sensor failed — or it's enabled with no sensor connected to the product 2 input |
6 codes link to a full section below. The other 16 are listed as the manufacturer's manual gives them. Every row comes from the manual cited at the end of this page.
What does each code mean — and what should you do?
DOOR AJAR ALARM — Door open too long
The door digital input has been active longer than the Door Al Delay setting, indicating the walk-in door has been left open or the door switch has failed.
What causes it:
- The walk-in door left open longer than the Door Al Delay setting
- A damaged gasket, closer, or latch — or ice on them — keeping the door from sealing
- A door switch failed, stuck, or out of alignment
Can staff fix it? Usually. Close the door fully, press ALARM to silence the buzzer, and check gasket, closer, latch, and switch alignment — that covers the common cases.
What to check, in order:
- Close the door fully and press the ALARM button to silence the buzzer
- Check the door gasket, closer, and latch for damage or ice
- Verify the door switch is aligned and not stuck
Why it takes a technician: If the alarm persists with the door genuinely closed, the switch or its wiring needs continuity testing — a short technician task, but meter work on the control circuit.
Source: Norlake — Programmable Controller — operation manual (113470 Rev. J, 6/20)
ROOM TEMP HIGH ALARM — Room air temperature above high limit
Room air temperature exceeded the user-set high alarm limit for longer than the alarm delay. Norlake notes this is an early warning that often occurs when the door is left open too long; closing the door and pressing ALARM delays the air alarm while temperature recovers.
What causes it:
- The door left open too long — Norlake flags this as the most common trigger for this early warning
- Ice on the evaporator coil or fans not running
- Condensing unit off or its coil airflow blocked
- A tripped breaker on the refrigeration circuit
Can staff fix it? Often. Close the door and press ALARM — that silences and deliberately delays the alarm while temperature recovers — then verify coil, fans, condensing unit, and breaker. Most of these resolve without a truck roll.
What to check, in order:
- Close the door and press the ALARM button to silence and delay the alarm
- Check the evaporator coil for ice and confirm the fans are running
- Confirm the condensing unit is running and its coil airflow is clear
- Check the breaker for the refrigeration circuit
Why it takes a technician: If the room doesn't come back to range after the door is closed and airflow verified, the remaining causes are refrigerant-side — sealed-system diagnosis under EPA Section 608 — and warm product doesn't wait.
Source: Norlake — Programmable Controller — operation manual (113470 Rev. J, 6/20)
ROOM TEMP LOW ALARM — Room air temperature below low limit
Room air temperature dropped below the user-set low alarm limit for longer than the alarm delay, indicating the room is overcooling.
What causes it:
- Setpoints changed on the SET screens
- A stuck cooling relay or contactor keeping refrigeration running past setpoint
- Freeze-sensitive product sitting in the evaporator discharge air
Can staff fix it? Partially. Verify the real temperature with a separate thermometer, check the SET screens for changed setpoints, and move freeze-sensitive product out of the discharge air.
What to check, in order:
- Verify the actual room temperature with a separate thermometer
- Check whether setpoints were recently changed on the SET screens
- Move freeze-sensitive product away from the evaporator discharge
Why it takes a technician: A room that keeps running below setpoint points at a stuck relay or contactor — live electrical diagnosis in the control panel — and in a cooler, sustained overcooling freezes product.
Source: Norlake — Programmable Controller — operation manual (113470 Rev. J, 6/20)
ROOM TEMPERATURE SENSOR FAILURE — Air temperature sensor failed
The room air sensor has failed. The status line will show "USING PROD SENSOR" if the controller falls back to the product sensor, or "SENSOR FAIL MODE" if all sensors have failed and the unit runs on timed Cool On/Heat On cycles.
What causes it:
- The room air sensor has failed outright
- The controller running on fallback — "USING PROD SENSOR" if the product sensor took over, or "SENSOR FAIL MODE" timed cycling if every sensor is gone
Can staff fix it? No — but staff should check the MENU 1 status line to see which fallback the controller is in, verify box temperature with a separate thermometer, and record both for the tech. Fallback keeps the room alive, not well-controlled.
What to check, in order:
- Check the MENU 1 status line to see which fallback mode the controller is in
- Verify box temperature with a separate thermometer
- Record the alarm and status for the service tech
Why it takes a technician: The room is running on backup control, which holds temperature roughly at best — timed cycling can drift either direction. The sensor needs testing and replacement promptly, before backup control turns into a product problem.
Source: Norlake — Programmable Controller — operation manual (113470 Rev. J, 6/20)
AIR FLOW LOSS 1 — Evaporator air flow lost
The air flow switch for circuit 1 has tripped, indicating the evaporator blower is not moving air. The alarm screen itself advises checking the blower and belts. (AIR FLOW LOSS 2 is the same alarm for the second circuit.)
What causes it:
- The evaporator blower for circuit 1 not moving air — the air flow switch tripped
- A tripped breaker on the evaporator fan circuit
- Ice physically blocking the fan blades or coil
- A failed blower motor or belt — the alarm screen itself says check blower and belts
Can staff fix it? Partially. Look at the evaporator — are the blades turning? Check the fan-circuit breaker and look for ice jamming the blades. A tripped breaker or visible ice block is staff-resolvable; a dead motor is not.
What to check, in order:
- Look at the evaporator: are the fan blades turning?
- Check the breaker for the evaporator fan circuit
- Check for ice blocking the fan blades or coil
Why it takes a technician: If the fans won't run with power confirmed on, motor, belt, or contactor replacement is a service job. With no air moving across the coil, the room stops cooling regardless of how well the refrigeration side works.
Source: Norlake — Programmable Controller — operation manual (113470 Rev. J, 6/20)
POWER RESTART — Power was interrupted
If the Power Reset Alarm is enabled, this alarm records that controller power was interrupted; it appears about 10 seconds after power-up. It does not affect control of the room — it only logs the outage.
What causes it:
- Controller power was interrupted and the Power Reset Alarm feature logged it — it appears about 10 seconds after power-up
- A building outage, or something more local like a failing breaker or wiring issue if it recurs without a known outage
Can staff fix it? Yes — this one is informational. Press ALARM to view and acknowledge it, confirm room and product temperatures recovered, and check whether other equipment on the circuit also blinked.
What to check, in order:
- Press the ALARM button to view and acknowledge the alarm
- Verify room and product temperatures recovered after the outage
- Check whether other equipment on the same circuit also lost power
Why it takes a technician: The alarm never affects control of the room. The only reason to bring in an electrician or tech is repeated power interruptions with no known outage — that pattern points at a failing breaker or wiring fault worth catching early.
Source: Norlake — Programmable Controller — operation manual (113470 Rev. J, 6/20)
How do you diagnose a Norlake programmable controller alarm, step by step?
- Silence, then read every screen. ALARM once for the buzzer, then step through all active alarms — more than one may be active.
- Check the status line for USING PROD SENSOR or SENSOR FAIL MODE (above).
- Most alarms come from digital inputs. Compressor 1 and 2 alarms, air flow 1 and 2, door, water, smoke, humidity and drain are all inputs, each configurable as normally open or normally closed; the alarm sounds when the input matches its "Active if" setting for longer than the delay. A wrongly configured or failed input device can raise an alarm even when the refrigeration is fine.
- AIR FLOW LOSS: look at the blower first. The alarm screen itself says Check Blower, Belts.
- Sensor failures: the standard air sensor is a 10k thermistor (10,000 Ω; a 1k RTD is optional), and the board's NTC inputs are 10 kΩ ±1 % at 25 °C. Sensor calibration offsets are under the AUX2 key — a sensor that reads slightly off can be offset, but a failed one must be replaced.
- POWER RESTART is informational. If enabled it appears 10 seconds after power-up, and the room keeps running on its configuration. The separate power-failure alarm uses a battery switch to the right of the user terminal: top = test, centre = off, bottom = on.
- Ring Back sets how many minutes the buzzer stays silent after an alarm is silenced — if it keeps coming back, the condition is still there.
Which parts are usually involved?
| Part | Codes that point to it | Note |
|---|---|---|
| Air temperature sensor (10k thermistor) | ROOM TEMPERATURE SENSOR FAILURE, ROOM TEMP HIGH ALARM, ROOM TEMP LOW ALARM | |
| Product temperature sensor(s) | PRODUCT TEMPERATURE SENSOR ALARM, PRODUCT 2 TEMPERATURE SENSOR FAILURE | |
| Evaporator blower, belts and air-flow switch | AIR FLOW LOSS 1, AIR FLOW LOSS 2 | |
| Compressor high / low pressure switches | COMPRESSOR 1 HIGH/LOW PRESSURE, COMPRESSOR 2 HIGH/LOW PRESSURE | |
| Door switch (digital input 7) | DOOR AJAR ALARM | |
| Drain-pan and water sensors | DRAIN PAN ALARM, WATER ALARM | |
| Smoke detection input | SMOKE DETECTION SYSTEM OFF | |
| Controller memory | EEPROM FAILURE | |
| Power-failure alarm battery | — | Test it with the switch in the top position: the buzzer sounds if the battery is OK. |
What refrigeration is behind these codes?
Every code here is the controller reporting a reading from the refrigeration system. The background is explained once, for every controller on this site: how a controller holds temperature — and how its sensors are tested; how defrost works and what goes wrong.
If it does come to a service call and you're in Nashville, TN or Birmingham, AL, we maintain independently compiled lists of local companies that service walk-in coolers — real businesses with verified contact information, none of whom paid to be listed.