What does alarm 'E0' mean on a Carel IR33 controller?

E0 on the Carel IR33 is not a standard alarm — the display shows 'E0' during initial power-up while the controller runs its self-check. If E0 persists, it may indicate a EEPROM fault (corrupt configuration). Perform a factory reset by holding SET+UP+DOWN together for 10 seconds, then reprogram the controller from scratch.

How do I access the Carel pCO5 supervisor from a laptop?

Connect to the Carel pCO5 via Ethernet (LAN port on the pCO5+ board). Open the pCO web server at the pCO's IP address using a web browser. For older pCO3 units, use the RS485 port with Carel's 'pCOterm' software or a MODBUS TCP gateway. The default IP is 192.168.1.100 unless changed during commissioning.

How do I set up the Carel heaterCOMPACT humidifier?

The Carel heaterCOMPACT is configured via its built-in display. Key settings: target humidity setpoint, dead band (proportional band), probe type (0-1V, 0-10V, or NTC), and cylinder type (set when changing the steam cylinder). Run the 'flush' procedure when installing a new cylinder to prime the water pump and check for leaks before enabling automatic operation.

What does Carel NTC sensor 'Er' or 'EEEE' mean?

Carel displays 'Er' or 'EEEE' when an NTC probe reads out of range — either open circuit (broken wire) or short circuit. For NTC 10kΩ probes: resistance should be 32.65kΩ at 0°C, 10kΩ at 25°C, and 3.54kΩ at 50°C. Test the probe in a glass of iced water at 0°C — a correct probe reads approximately 32kΩ.

How do I update firmware on a Carel pCO controller?

Carel pCO firmware updates require a USB memory stick formatted to FAT32 with the firmware file placed in the root directory. Power off the pCO, insert the USB stick, power on while holding the USER button until the LED flashes. The controller copies the firmware automatically. Do not power off during the update. After the update, verify the firmware version in the pCO Service menu.

What does E1 mean on a Carel ir33 / SmartCella / UltraCella controller?

E1 on Carel ir33, SmartCella and UltraCella refrigeration controllers indicates that probe S1 (the room or cabinet probe) has failed open-circuit, short-circuit, or out-of-range, so the controller cannot read the temperature it uses for primary regulation. Disconnect S1 and measure NTC resistance against the Carel R-vs-T table (a 10 kΩ NTC reads about 32 kΩ at 0 °C and 10 kΩ at 25 °C); replace the probe if open or shorted. The companion E2 alarm flags the defrost / evaporator probe S2 with the same diagnostic procedure. Re-route probe cables at least 3 cm away from power conductors to avoid recurrence.

What does AL01 mean on a Carel µChiller or pCO chiller controller?

AL01 on Carel µChiller and pCO chiller controllers signals that the compressor 1 thermal overload protection has tripped — the motor drew excessive current and the overload device opened its contact. Wait at least 15–20 minutes for the compressor and overload to cool before resetting. Inspect the condenser for fouling, measure discharge pressure with refrigerant gauges, and check compressor running current with a clamp ammeter against nameplate FLA. AL01 is manual-reset; clearing it without identifying the root cause (dirty condenser, low charge, weak winding) will trip again on the next cycle.

How do I clear a manual-reset alarm on a Carel controller?

Carel alarms come in two flavours: automatic-reset (HI, LO, E1–E14, AL06, AL10) clear themselves once the underlying condition resolves; manual-reset alarms (AL01 thermal overload, AL03 high-pressure switch, AL09 low-pressure switch, AL20–AL34 probe B-faults) require the technician to fix the fault first, then press and hold the Prg / alarm button on the controller for 2–3 seconds. Some safety alarms latched on a physical switch (HP / LP cutouts, anti-freeze stat) also require resetting the device itself before the controller will allow restart. Power-cycling alone does not clear latched manual-reset alarms.

What's the difference between Carel ir33, pCO, µChiller, and heaterCOMPACT fault codes?

Carel uses different code dictionaries by controller family. ir33 / SmartCella / UltraCella for retail and walk-in refrigeration use E1–E14 for probe faults plus HI / LO / EE / IA. pCO programmable controllers (pCO3, pCO5, pCO5+) running OEM applications expose application-specific codes plus the same probe-fault scheme. µChiller and pCO chiller applications use AL01–AL77 for compressor, pressure-switch and probe alarms. heaterCOMPACT and humiSteam humidifiers use E1–E9 for steam-cylinder, water-conductivity and current-fault conditions. Always confirm which controller family is installed before consulting a code table.

What does LP1 / AL10 mean on a Carel heat pump?

LP1 (or AL10 on chiller-style controllers) is a low-pressure switch trip on compressor 1 in heating mode. The LP switch monitors suction pressure on the heat-pump cycle; when outdoor ambient drops below the unit's rated heating range, refrigerant charge is low, the outdoor coil is iced over, or the outdoor fan has failed, suction pressure falls below the cutout and the controller shuts down the compressor. Record the outdoor ambient, connect refrigerant gauges to verify the fault is real, inspect the outdoor coil and fan, and leak-test if charge is low. Do not repeatedly reset and restart — vapor-starved operation rapidly damages compressor bearings.

Quick Answer

Carel controllers display family-specific fault codes. On ir33 / SmartCella / UltraCella refrigeration controllers, E1–E14 flag NTC and serial probe faults, HI / LO mark high and low temperature alarms, and EE signals an EEPROM error. On µChiller and pCO chiller controllers, AL01–AL77 cover compressor overloads, HP / LP pressure trips, and probe B1–B8 faults.

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By Nichita Herput

Co-founder & CEO · Reviewed May 2026

What error codes does Carel display?

Probe S1 (room / cabinet) fault on ir33 / SmartCella — measure NTC resistance and replace probe

Probe S2 (defrost / evaporator) fault — check sensor wiring and resistance against Carel R-vs-T table

E11

Serial probe S11 not updated — check RS-485 bus wiring, termination and probe address

High-temperature alarm — inspect door seals, condenser cleanliness and fan operation

Low-temperature alarm — verify setpoint, alarm differential (AL parameter) and probe location

EEPROM memory error — power-cycle, re-enter parameters, replace controller if persistent

AL01

Compressor 1 thermal overload — cool 15–20 min, clean condenser, check FLA before manual reset

AL03

Compressor 2 high-pressure switch trip — inspect condenser airflow and gauge discharge pressure

AL10

Compressor 1 low-pressure switch trip in heating — check outdoor ambient, charge and outdoor coil

AL20

Probe B1 fault on µChiller / pCO — check wiring at controller terminal and replace NTC if out of range

Common questions about Carel equipment

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