What do Heatcraft intelliGen (Bohn / Larkin) AL, ER and IN codes mean?
Part of the Heatcraft (Bohn/Larkin) walk-in controller codes hub. Same brand, different controller: Heatcraft Beacon II.
Short answer: intelliGen shows the code on the unit's OLED display and backs it with a light bar. Green is normal. An error (ER code) on any evaporator turns every light bar on the system yellow, with the unit that has the problem flashing yellow; an alarm (AL code) turns them all red, with the unit causing it flashing red. IN codes are information about conditions worth correcting, such as too many or too few defrosts.
Which machines use it?
The intelliGen refrigeration controller is Heatcraft's current-generation control system, factory-fitted to unit coolers sold under Heatcraft's brands — Bohn and Larkin most commonly, along with Climate Control and Chandler. If your walk-in's evaporator carries one of those nameplates and shows a small OLED text display with a colored light bar, this is your controller. It reports with AL (alarm), ER (error), and IN (information) codes on the display, backed by the light bar: green is normal, yellow is a non-critical fault, red means act now. On newer A2L-refrigerant unit coolers it also runs the built-in refrigerant leak detection system. Practical tip: photograph the display before power-cycling — the code and light bar color together tell the technician most of the story.
How do you read and clear the display?
Before chasing a code, check the unit isn't in Service or Product Load mode — both pump the system down and switch off the expansion valve, fans and heaters, which looks exactly like a failure. The Monitor menu shows live sensor readings, and every board logs box temperature, coil temperature, suction pressure and temperature, superheat, valve steps, door switch and volts every minute for 60 days — the log copies to a USB drive for the technician.
How do you enter the parameter menu?
You work the intelliGen from the iRC user interface (iRC UI) on the evaporator: a Home button, a Return button, a Control Knob that turns to scroll and presses to select, and a Favorites button beside the status light bar. Press Home and the top-level menus are: MONITOR, ALARMS, BOX SETTINGS, SUPERHEAT CONTROL, DEFROST SETTINGS, EV FAN, EXV, CONNECTIVITY, GENERAL SETTINGS, MANUAL, CALIBRATION, USB OPERATION and SECURITY. Monitor is read-only — that's the one to open first when a code is showing, because it gives live box, coil, suction and superheat readings without any risk of changing anything.
Navigating: turn the knob until the menu you want is displayed and press to open it. The first item appears; turn to see the choices for that set point, press to select, and the next item comes up. Return takes you back to the beginning of the current menu; Home goes to the main menu (the manual's service procedures say press Home twice to be sure you're at the top).
PINs: two are set in the iRC — Basic (factory default 888888) and Expert (factory default 999999). Both can be changed, and local or remote access can be blocked, under SECURITY. Each set point in the manual is tagged with the mode it needs — running or service. Service-mode changes pump the system down; the iRC enters Service automatically when a protected item is chosen (it can take up to 2 minutes, showing "Entering Service Mode... please wait") and you leave it through BOX SETTINGS › SERVICE MODE › Exit. Some set points are system parameters (change them from any evaporator's iRC and they apply to all) and some are local (only from that evaporator's own iRC), which matters on multi-evaporator boxes.
Every Heatcraft intelliGen code at a glance
| Code | What it means |
|---|---|
| AL01 | High box temperature alarm |
| AL02 | Low box temperature alarm |
| AL03 | System startup failure |
| AL04 | Input fault (sensor failure alarm) |
| AL06 | Door open alarm |
| AL10 | LL high box temperature |
| AL11 | LL low box temperature |
| AL12 | A2L refrigerant leak mitigation active |
| ER01 | Box temperature sensor error |
| ER02 | Coil temperature sensor error |
| ER03 | Evaporator suction temperature sensor error |
| ER04 | Evaporator suction pressure transducer error |
| ER11 | Control circuit error (condensing unit safety tripped) |
| ER13 | Spare I/O error |
| ER14 | Power supply voltage low |
| ER15 | Power supply voltage high |
| ER16 | Low superheat error |
| ER18 | Auxiliary temperature probe error |
| ER19 | Replace controller clock battery |
| ER20 | Log disrupted — pull the data log to confirm missing data, then power cycle |
| ER22 | User interface (iRC UI) failure |
| ER23 | Board communication error |
| ER24 | Aux temp override — the aux temperature sensor was assigned to two functions; no action required |
| ER25 | System connection lost (multi-evaporator communication) |
| ER26 | EV (evaporator) connection lost |
| ER27 | High humidity |
| ER28 | Low humidity |
| ER29 | Humidity sensor error |
| ER31 | LL connection lost — the three digits shown are the last 3 digits of the disconnected system's IP address |
| ER32 | A2L refrigerant early warning |
| ER33 | A2L sensor fault |
| ER34 | A2L service (X = leak-detection sensor number) |
| ER35 | A2L mitigation (X = leak-detection sensor number) |
| ER36 | A2L refrigerant mismatch |
| ER37 | A2L mitigation controller communication loss — check the RS-485 wiring and its polarity |
| IN01 | Too many defrosts (information code) |
| IN05 | Too few defrosts — 8 consecutive defrosts ended on time information |
20 codes link to a full section below. The other 17 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?
AL01 — High box temperature alarm
The walk-in box temperature has stayed above the programmed High Box Temperature alarm setpoint (default 50F cooler / 40F freezer) longer than the alarm delay time (default 60 minutes). The light bar turns red and AL01 shows on the OLED display.
What causes it:
- A door left open or a leaking gasket loading the box with warm, humid air
- Warm product just loaded into the box, raising air temperature temporarily
- Heavy ice on the evaporator coil choking airflow across it
- Condensing unit not doing its job — tripped breaker, dead fans, or a dirty/blocked condenser coil
- Unit left in Service or Product Load mode so it isn't cooling normally
Can staff fix it? Often, yes. Doors, gaskets, recent loading, blocked condenser airflow, and a forgotten Service mode are all things staff can find and fix in minutes without opening a panel.
What to check, in order:
- Check that all doors are fully closed and door gaskets seal tight
- Ask staff whether product was just loaded — warm product can trip this alarm temporarily
- Look at the evaporator coil inside the box for heavy ice buildup
- Check the outdoor/condensing unit: breaker on, fans spinning, coil free of dirt, leaves and boxes blocking airflow
- Verify no one left the unit in Service or Product Load mode
Why it takes a technician: If the box isn't pulling down within an hour of those checks, the problem is inside the sealed system or the controls — refrigerant diagnosis requires gauges and EPA Section 608 certification, and every hour above temperature puts product at risk.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
AL02 — Low box temperature alarm
Box temperature has dropped below the Low Box Temperature alarm setpoint (default 30F cooler / 20F freezer) for longer than the alarm delay time. In a cooler this risks freezing product.
What causes it:
- The box temperature setpoint was changed, accidentally or otherwise
- The system keeps running too cold because the temperature sensor or control is misreading
- Product sitting directly in the evaporator discharge air, where it can freeze even when the box average is fine
Can staff fix it? Partially. Staff can verify the setpoint, compare the display against a separate thermometer, and move product out of the cold airstream — that resolves the setpoint and product-placement cases.
What to check, in order:
- Verify the box temperature setpoint was not accidentally changed on the controller
- Move product away from the evaporator discharge air if it is freezing
- Note the displayed box temp and compare it against a separate thermometer in the box
Why it takes a technician: If the setpoint is right and the box still overcools, a sensor or control is lying to the system. Testing a sensor against a reference and replacing it is controller-level work, and in a cooler continued overcooling freezes and ruins product.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
AL03 — System startup failure
Shown only when the condensing unit control circuit is wired to the controller. The system pumped down and could not restart — typically a compressor safety (high/low pressure, oil pressure) keeps tripping.
What causes it:
- A compressor safety — high pressure, low pressure, or oil pressure — tripping every time the system tries to restart
- Dirty or blocked condenser coil, or dead condenser fans, driving pressures out of range
- Power problem at the condensing unit — breaker or disconnect off
Can staff fix it? Only the easy outer layer: staff can confirm the breaker is on, clear junk stacked around the condensing unit, and check that the fans spin and the coil is clean. If it still won't restart, it's a service call.
What to check, in order:
- Check the condensing unit breaker and disconnect are on
- Check the condenser coil for dirt and blocked airflow, and confirm condenser fans run
- Make sure nothing is stacked around the condensing unit restricting air
Why it takes a technician: Identifying which safety is tripping — pressure, oil, or refrigerant-related — takes gauges, electrical testing, and training. Meanwhile the system is pumped down and not cooling, so this is a same-day, product-at-risk call.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
AL04 — Input fault (sensor failure alarm)
One of the key control inputs — box temperature sensor (ER01), suction temperature sensor (ER03), or suction pressure transducer (ER04) — has failed or is disconnected, so the controller cannot run the system normally.
What causes it:
- Box temperature sensor failed or disconnected (companion code ER01)
- Suction temperature sensor failed or disconnected (companion code ER03)
- Suction pressure transducer failed or disconnected (companion code ER04)
- A transient glitch that a single power cycle may clear
Can staff fix it? Barely. Staff can read off the companion ER code, power-cycle once at the breaker, and log the box temperature — that's the extent of it. The failed part still has to be tested and replaced.
What to check, in order:
- Check the controller display for the companion error code (ER01, ER03 or ER04) to identify which sensor faulted
- Power-cycle the unit at the breaker once to see if the fault clears
- Record the code and the box temperature for the service call
Why it takes a technician: The controller can't run the system properly without these inputs. A sensor gets tested against a reference and replaced; a pressure transducer is refrigerant-side work requiring gauges and EPA Section 608 certification. Same-day call — the system is running blind.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
AL06 — Door open alarm
The walk-in door switch has reported the door open longer than the programmed Door Open Alarm Time (default 60 minutes). A related high box temperature alarm may follow.
What causes it:
- The door was genuinely left open past the alarm delay — pallets, cords, or product propping it
- A damaged gasket or sweep keeping the door from sealing and latching
- The door switch on the frame knocked loose or misaligned so it reports open even when the door is shut
Can staff fix it? Usually, yes. Closing the door, clearing whatever propped it, and re-seating a knocked-loose switch are all staff-level fixes. A torn gasket is a cheap, orderable part.
What to check, in order:
- Close the walk-in door fully and confirm it latches
- Check the door gasket and sweep for damage that keeps the door from sealing
- Check that nothing (pallets, cords, product) is propping the door open
- Verify the door switch on the frame is not knocked loose or misaligned
Why it takes a technician: If the alarm stays on with the door verifiably closed, the switch itself or its normally-open/normally-closed configuration in the controller is wrong — checking and reconfiguring that is electrical and settings work a technician should do.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
AL12 — A2L refrigerant leak mitigation active
On A2L-refrigerant unit coolers, the Refrigerant Detection System (RDS) has measured a refrigerant concentration at the regulatory mitigation level and has taken over the unit to run mitigation actions. The light bar turns red.
What causes it:
- A probable leak of A2L (mildly flammable) refrigerant — the detection system has measured concentration at the regulatory mitigation level
- The controller has taken over the unit to run mitigation, which is why normal operation stopped
Can staff fix it? No. The only correct staff actions are keeping people out of the box, ventilating the area, keeping ignition sources away, and NOT silencing or bypassing the alarm. Do not attempt anything else.
What to check, in order:
- Keep people out of the walk-in box and ventilate the area
- Do not create ignition sources near the unit (open flames, sparking tools)
- Do not silence or bypass the alarm
Why it takes a technician: A2L refrigerants are mildly flammable — a leak is a safety event, not just a cooling problem. Finding and repairing the leak and recharging the system is legally restricted to EPA Section 608 certified technicians. Call immediately.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER01 — Box temperature sensor error
The room/box temperature sensor is reading out of range, shorted, or disconnected. The light bar shows yellow and the controller may fall back to another sensor to keep running.
What causes it:
- The box temperature sensor reading out of range, shorted, or disconnected
- A transient fault that one power cycle may clear
- Sensor wiring disturbed — which is why the manual says don't unplug or reroute it yourself
Can staff fix it? Not really. Staff can confirm the box is still holding temperature with a separate thermometer and try one power cycle. The sensor itself has to be tested against a reference and replaced if it disagrees.
What to check, in order:
- Note whether the box is still holding temperature with a separate thermometer
- Power-cycle at the breaker once to see if the error clears
- Do not unplug or reroute sensor wiring yourself
Why it takes a technician: The controller may be running on a fallback sensor, which is a degraded state, not a fix. Testing the sensor's reading against a reference thermometer and replacing it is exactly what the manual prescribes — controller-level work for a technician.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER02 — Coil temperature sensor error
The evaporator coil (defrost termination) sensor has failed or is disconnected. Defrost cycles may not terminate correctly, which can lead to an iced-up coil.
What causes it:
- The evaporator coil (defrost termination) sensor failed or disconnected
- Because defrost can no longer end on coil temperature, the coil may progressively ice up
Can staff fix it? No — staff can only watch: check the coil for ice, note how often defrosts run, and record the code. The sensor has to be checked and replaced.
What to check, in order:
- Visually check the evaporator coil for ice buildup
- Note how often the unit has been going into defrost
- Record the error and box temperature for the service visit
Why it takes a technician: The manual's fix is to test the sensor and its connections and replace as needed. Left alone, a coil that ices over stops cooling the box, so this needs a scheduled service visit before it becomes a high-temperature emergency.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER03 — Evaporator suction temperature sensor error
The suction line temperature sensor at the evaporator has failed or is disconnected. The controller uses this sensor to calculate superheat and drive the electric expansion valve, so cooling control is degraded.
What causes it:
- The suction line temperature sensor at the evaporator failed or disconnected
- With it gone, the controller can't calculate superheat to drive the electric expansion valve, so cooling control is degraded
- A transient fault a single power cycle may clear
Can staff fix it? No. Confirm the box is holding temperature, try one power cycle, and log the code — that's the staff-side limit.
What to check, in order:
- Confirm the box is still holding temperature
- Power-cycle once at the breaker to see if the error clears
- Log the code for the technician
Why it takes a technician: Superheat control protects the compressor; running degraded risks the most expensive component in the system. Testing and replacing the sensor and verifying superheat afterward is refrigeration-tech work.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER04 — Evaporator suction pressure transducer error
The suction pressure transducer has failed or is disconnected. Like ER03, this breaks the controller's superheat calculation for the expansion valve.
What causes it:
- The suction pressure transducer failed or disconnected
- The controller has lost its superheat calculation for the expansion valve, same consequence as ER03
- A transient fault a power cycle may clear
Can staff fix it? No. Staff can confirm the box is holding temperature, note any warming trend, and power-cycle once. Do not touch the refrigerant lines or the transducer itself.
What to check, in order:
- Confirm the box is holding temperature and note any warming trend
- Power-cycle once at the breaker
- Do not touch refrigerant lines or the transducer
Why it takes a technician: A pressure transducer lives on the refrigerant side of the system. Replacing it means opening sealed refrigerant connections — legally EPA Section 608 certified work, done with gauges.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER11 — Control circuit error (condensing unit safety tripped)
Shown only when the condensing unit is wired to the controller. A safety in the condensing unit control circuit has opened — the manual lists low pressure, high pressure, oil pressure, compressor module, or phase loss as causes.
What causes it:
- A condensing unit safety opened — the manual lists low pressure, high pressure, oil pressure, compressor module, or phase loss
- Dirty condenser coil or blocked/dead condenser fans driving head pressure up
- Heavy evaporator icing starving the system on the low side
- Power problem at the condensing unit
Can staff fix it? Only the airflow layer: staff can verify power, clean-coil, and running-fans, and note whether the compressor is short-cycling. Which safety actually tripped can't be determined from the display.
What to check, in order:
- Check the condensing unit breaker and power
- Check the condenser coil is clean and its fans are running with unobstructed airflow
- Look at the evaporator coil for heavy icing
- Note whether the compressor is short-cycling (starting and stopping repeatedly)
Why it takes a technician: Diagnosing whether it was pressure, oil, or phase loss requires gauges on the refrigerant circuit and live electrical testing at the condensing unit — both technician territory, and repeated safety trips will eventually take the compressor down.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER14 — Power supply voltage low
The 24V control power feeding the iRC board has dropped below the minimum (about 22V per the manual). Usually a building supply-voltage or transformer issue.
What causes it:
- Building supply voltage sagging — a brownout, often at heavy-load times of day
- The control transformer on the wrong tap, delivering under ~22V to the board
- A breaker not fully on
Can staff fix it? Staff can gather the evidence — is other equipment on the circuit acting up, is the breaker fully on, does it happen at certain times of day — but can't fix supply voltage.
What to check, in order:
- Check whether other equipment on the same circuit is also acting up (brownout clue)
- Check the breaker feeding the unit is fully on
- Note whether the error appears at certain times of day (heavy building load)
Why it takes a technician: Measuring primary power and changing the control transformer tap is live electrical work inside the panel. Chronic undervoltage also stresses the control board, so it's worth an electrician or tech visit before something more expensive fails.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER15 — Power supply voltage high
The 24V control power feeding the iRC board is above the maximum (about 30V per the manual), usually a wrong transformer tap or high building voltage.
What causes it:
- Control transformer on the wrong tap, feeding the board above ~30V
- High building supply voltage
Can staff fix it? No. Record when the error occurs and whether it's constant or intermittent — and don't open the control panel. That's it.
What to check, in order:
- Record when the error occurs and whether it is constant or intermittent
- Do not open the control panel
Why it takes a technician: Overvoltage can cook the control board, so this isn't a wait-and-see item. Verifying supply voltage and moving the transformer tap is live electrical work for a technician or electrician.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER16 — Low superheat error
The controller measured suction superheat below its minimum safe value for 2 minutes; it shuts the unit down briefly, displays the error, then restarts. Causes in the manual include an iced coil, expansion valve problems, or a bad sensor reading.
What causes it:
- An iced-up evaporator coil starving the system
- Expansion valve problems keeping superheat below the safe minimum
- A bad sensor reading feeding the superheat calculation
- Evaporator fans not running
Can staff fix it? Partially. Staff can check the coil for ice, confirm the fans run, and note whether the unit keeps stopping and restarting — a lightly iced coil that defrosts out may end the problem. A repeating ER16 is a service call.
What to check, in order:
- Visually check the evaporator coil for ice buildup
- Note whether the unit keeps stopping and restarting
- Confirm evaporator fans are running
Why it takes a technician: Persistent low superheat means liquid refrigerant can flood back to the compressor and destroy it — the most expensive failure a walk-in can have. Diagnosing valve and sensor causes takes gauges and EPA Section 608 certified refrigerant work.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER19 — Replace controller clock battery
The coin-cell battery that keeps the controller's clock is low or missing. The system still cools, but time-based logs and defrost schedules can be affected after a power loss.
What causes it:
- The coin-cell clock battery on the control board is low or missing
- After a power loss, time-based logs and defrost schedules can drift because the clock isn't held
Can staff fix it? Effectively yes, in the sense that nothing is urgent: cooling is not at risk. Note it and fold the battery swap into the next scheduled service visit rather than paying for an emergency call.
What to check, in order:
- Note the error — cooling is not immediately at risk
- Schedule the battery replacement rather than treating it as an emergency
Why it takes a technician: The battery lives on the control board inside the panel, so the manual routes replacement through a technician — but it's a next-visit item, not an emergency.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER22 — User interface (iRC UI) failure
The controller board has lost proper communication with its display/user interface module, usually a ribbon-cable connection issue per the manual.
What causes it:
- The controller board lost communication with its display/user interface module
- Per the manual, usually a ribbon-cable connection issue between board and display
Can staff fix it? One shot: power-cycle at the breaker and check whether the unit is still cooling normally despite the dead display. If the error persists, it needs hands inside the panel.
What to check, in order:
- Power-cycle the unit once at the breaker
- Check whether the unit is still cooling normally despite the display fault
Why it takes a technician: Reseating or replacing the UI ribbon harness or the display module means opening the control enclosure — a technician job. The good news is the refrigeration usually keeps running while you wait.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER23 — Board communication error
Communication between the iRC control board and the user interface has faulted. The manual's remedy is checking the ribbon cable and power-cycling.
What causes it:
- Communication fault between the iRC control board and the user interface
- Ribbon cable connection issue — the manual's named remedy is checking it and power-cycling
Can staff fix it? Try one power cycle at the breaker and confirm the unit still cools. If the error returns, staff have done all they safely can.
What to check, in order:
- Power-cycle the unit once at the breaker
- Confirm the unit still cools and note if the error returns
Why it takes a technician: A returning ER23 means the ribbon connection or one of the boards needs inspection inside the control panel — panel-open work for a technician, though usually not a cooling emergency.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER25 — System connection lost (multi-evaporator communication)
An evaporator controller on a multi-unit system lost its communication link with the rest of the system — typically damaged, reversed-polarity, or improperly shielded communication wiring per the manual.
What causes it:
- An evaporator controller on a multi-unit system lost its communication link
- Communication wiring damaged, reversed polarity, or improperly shielded — per the manual
- A comm cable pinched, unplugged, or disturbed during other work in the box
Can staff fix it? Partially. Power-cycle the affected unit, look for a cable someone obviously knocked loose during recent work, and note which evaporator's light bar is flashing. Anything beyond a visibly unplugged cable is wiring diagnosis.
What to check, in order:
- Power-cycle the affected unit once
- Check that no communication cable was recently disturbed, pinched, or unplugged during other work
- Note which evaporator's light bar is flashing
Why it takes a technician: Checking communication wiring polarity and shield grounding across a multi-evaporator system takes a meter and knowledge of the network layout — a controls-savvy technician's job.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
ER32 — A2L refrigerant early warning
The Refrigerant Detection System on an A2L unit cooler has detected refrigerant at an early-warning level; the display shows a yellow light bar. The manual directs checking unit cooler piping for leaks (the code's -X suffix identifies which leak sensor).
What causes it:
- The refrigerant detection system on an A2L unit cooler has sensed refrigerant at its early-warning level — a likely developing leak in the unit cooler piping
- The -X suffix on the code identifies which leak sensor tripped
Can staff fix it? No. Ventilate the area, limit access to the box, keep ignition sources away, and do not reset or bypass the detection system. This is a leak until proven otherwise.
What to check, in order:
- Ventilate the area and limit access to the walk-in box
- Avoid ignition sources near the equipment
- Do not reset or bypass the detection system yourself
Why it takes a technician: A2L refrigerants are mildly flammable, and leak repair plus recharge is EPA Section 608 certified work by law. Early warning is the cheap moment to fix it — before it escalates to full mitigation shutdown (AL12).
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
IN01 — Too many defrosts (information code)
Informational notice: the unit has run 8 consecutive defrost cycles that each lasted under 5 minutes, suggesting the defrost schedule is more frequent than the coil needs.
What causes it:
- The defrost schedule is running more often than the coil actually needs — 8 straight defrosts each finished in under 5 minutes
- Purely informational; nothing has failed
Can staff fix it? Yes, in the sense that no action is needed today. Confirm the coil stays clear of ice between defrosts and jot down the current schedule for the next service visit.
What to check, in order:
- Visually confirm the coil is staying clear of ice between defrosts
- Note the current defrost schedule shown on the controller for the technician
Why it takes a technician: Optimizing the defrost schedule is a controller-settings change best made by the servicing technician, because a schedule set too lean on the other side lets the coil ice up. It's a next-visit optimization, not an emergency.
Source: Heatcraft Refrigeration Products — intelliGen Refrigeration Controller — installation and operation manual (H-IM-iRC, February 2025)
How do you diagnose a Heatcraft intelliGen alarm, step by step?
- Find the flashing unit. On a multi-evaporator system every light bar changes colour, but only the unit with the problem flashes — go to that one and read its display.
- Rule out Service and Product Load mode (see above).
- Sensor codes (ER01–ER04, AL04): compare before replacing. Read the suspect sensor in the Monitor menu and compare it with a thermometer at the same spot. Or test it in stirred ice water: at 32 °F it should read 32,650 Ω — more than about 1,000 Ω off, replace it. Sensors don't need to be removed from the evaporator for checking.
- ER16 low superheat. intelliGen raises it when a board runs below the minimum superheat setting for 2 minutes. Check for an iced coil and the refrigerant type setting, then whether the expansion valve closes: pump the system down with the liquid-line valve closed, put the system in Service mode, reopen the liquid valve — if suction pressure rises, the valve is leaking.
- Box won't reach temperature (AL01 with the system running): Heatcraft's own sequence is — system running? refrigerant charge, operating superheat, high superheat with the valve wide open, low-pressure switch, equipment capacity against the load, box setpoint, compressor, condenser coil dirt, non-condensables, condenser fan, refrigerant type setting, iced coil, defrost settings, superheat setpoint, and °F/°C display.
- A2L units: AL12 and ER32–ER37 are leak-detection events. Units with A2L refrigerant carry a refrigerant detection system; when a leak reaches the mitigation level it takes over and the display shows AL12. Follow the unit's A2L safety instructions and call a technician.
- ER19: replace the clock battery — a coin cell on the iRC board.
- Pull the log. Errors and alarms are logged as they start and end (up to 500 entries) — copy them to USB so the technician sees the history, not just the current code.
Which parts are usually involved?
| Part | Codes that point to it | Note |
|---|---|---|
| Box (room) temperature sensor | ER01, AL01, AL02, AL04 | |
| Coil temperature sensor | ER02, IN01, IN05 | |
| Evaporator suction temperature sensor | ER03, ER16, AL04 | |
| Suction pressure transducer | ER04, AL04 | Factory intelliGen systems use the 300 psia transducer; the 139.7 psia setting is for Beacon II and QRC retrofits. |
| Electronic expansion valve (EXV) | ER16, AL01 | |
| Condensing-unit safety circuit and compressor | ER11, AL03 | |
| 24 V transformer and supply | ER14, ER15 | On a 208 V supply the transformer must be on the 208 V tap. |
| iRC board, iRC user interface and ribbon cable | ER22, ER23 | |
| Clock coin-cell battery | ER19 | |
| Door switch | AL06 | |
| Communication wiring between units | ER25, ER26, ER31 | |
| A2L refrigerant detection system (A2L units) | AL12, ER32, ER33, ER34, ER35, ER36, ER37 |
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: what superheat is and why controllers alarm on it; how defrost works and what goes wrong; refrigerants and the A2L change; how a controller holds temperature — and how its sensors are tested.
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.