The Carel µC²SE (µchiller²SE) is a controller, not a make of chiller. It is fitted by many process chiller manufacturers, so the same codes turn up on machines carrying very different badges.
HP1, LP1, A1, FL, tP, E1 to E4 and the EVD driver alarms: what each one means, what causes it on site, and whether it is safe to reset.
Quick answer
On a Carel µC²SE, HP1 is high pressure, LP1 is low pressure, A1 is the antifreeze alarm, FL is the flow switch, tP is a general thermal overload and E1 to E4 are probe faults. Codes starting with E, S, n, L or H followed by a 1, such as Ed1 or SH1, come from the electronic expansion valve driver rather than the chiller itself.
Carel supply the µC²SE to machine builders rather than to end users, so it appears inside process chillers from a range of manufacturers. We see it on Galletti units, on some MTA TAEevo variants, and on plenty of others besides.
Being straight about it: which controller sits behind a given badge is a minefield. Manufacturers change controller between model years, between sizes within a range, and sometimes between batches. Two chillers of the same make and model bought two years apart can show completely different codes. That is exactly why we organise this library by the controller as well as by the make.
If the controller on your panel has a three-digit display, four keys marked Prg/mute, Sel and two arrows, and a snowflake symbol, there is a good chance it is a µC²SE or a close relative. If you are not sure, send us a photo and we will tell you.
Because the machine builder configures the parameters, the exact behaviour behind a code can vary between makes. The meanings below are Carel’s, and the causes are what we find on site.
Alarms are shown on the display with the red alarm LED lit. To reset manually, press and hold the up and down arrow keys together for 5 seconds.
Whether an alarm resets automatically or needs that manual reset is set by parameter P05, which the machine builder chooses. Some options make high and low pressure automatic for the first few trips in an hour, then manual after that. If an alarm will not clear, the condition causing it is still present.
| Code | Meaning | What usually causes it | Who can deal with it |
|---|---|---|---|
| HP1 | High pressure | Dirty or blocked condenser coil, failed condenser fan, high ambient, or recirculating warm air. The compressors stop immediately, ignoring the usual protection timers, and the condenser fan runs at full speed for 60 seconds to pull the pressure down. On units with a pressure transducer, it can also trigger from the high pressure threshold before the switch itself trips. | Site team can check the coil, fans and airflow. Engineer for the rest |
| LP1 | Low pressure | Usually refrigerant loss through a leak. Also a failing expansion device, a blocked drier or ice on the evaporator. The alarm is delayed after compressor start to avoid nuisance trips. | F-Gas engineer needed |
| A1 | Antifreeze alarm | Water leaving the evaporator is approaching freezing, measured on the outlet probe, or on evaporation temperature where an expansion valve driver is fitted. Low flow, weak or missing glycol, or a probe fault. The compressors stop immediately while the condenser fan and alarm relay activate. In standby the alarm is not detected, only the heaters are managed. | Site team can check flow and glycol. Engineer if it repeats |
| FL | Flow switch alarm | Detected only when the pump is running. Blocked strainer, closed valve, airlocked or failing pump, or a flow switch fault. Everything stops: pump, compressor and condenser fan. | Site team can check the strainer, valves and pump |
| tP | General thermal overload | An overload wired to the controller has tripped. Compressors, pumps and fans stop or are prevented from starting. | Engineer needed |
| tC1 | Circuit thermal overload | Thermal protection on the circuit, typically the compressor or its contactor. | Engineer needed |
| LA | General warning | A generic warning from a digital input, which does not change how the unit runs but does energise the alarm relay. What it means depends on what the machine builder wired to it, so check the drawing. | Engineer needed |
| Ht / Lt | High and low temperature warnings | Water temperature outside the configured band. Whether the compressor stops depends on a parameter the builder sets. Often load related, or a sign the machine is struggling. | Site team can check load, engineer if it persists |
| AHt / ALt | High or low temperature at start-up | Temperature outside limits when the plant is started, for example a hot fill after a shutdown. Display warning only. | Usually clears on its own |
| PH1 | Unloading due to high pressure | Not a fault. The controller has shed a stage of capacity to avoid a high pressure trip, and will bring it back when pressure falls. | Investigate condenser cleanliness at next service |
| L | Low load warning | The compressor is cycling on very short runs, so the controller has entered its low load logic. Common where the system water volume is small for the duty. | Engineer needed if cycling is frequent |
Not sure whether it is safe to reset? Send us a photo of the display and the data plate and we will tell you what it needs before anyone travels. Call 0121 820 8946.
| Code | Meaning | What usually causes it | Who can deal with it |
|---|---|---|---|
| E1 / E2 / E3 / E4 | Probe B1 to B4 faults | A damaged probe, a broken or disconnected cable, or a reading outside the expected range. E1 is the evaporator inlet probe and E2 the outlet, so those two usually stop the machine. Detected even in standby. | Engineer needed |
| EPr / EPb | EEPROM errors | The controller has a memory problem. With EPr it keeps running on data held in volatile memory, but the configuration is lost if power is interrupted. EPb at switch-on leaves the controller blocked. | Engineer needed, urgently for EPr |
| ELS / EHS | Low and high supply voltage | Supply voltage outside limits. High voltage switches off all energised relays; low voltage prevents loads starting. Usually a site supply issue rather than a chiller fault. | Site electrician |
| EL1 | Zero crossing error | The controller cannot read the supply waveform properly, so fan speed control is unreliable. The fans are driven at full speed as a precaution. Often supply noise or a wiring issue. | Engineer needed |
| I/O | Communication error with the I/O expansion board | The controller has lost the expansion board. Everything switches off. Cable, connector or board fault. | Engineer needed |
| Hc1 / Hc2 | Compressor or pump hours warning | Running hours past the maintenance threshold. A reminder, not a fault. | Raise at next service |
| Ad1 to Ad5 | Expansion board digital input alarms or warnings | Whatever the machine builder wired to those inputs, for example a leak detector, a phase monitor or an external interlock. As an alarm they stop the unit; as a warning they only display. Check the wiring diagram. | Engineer needed |
These appear only where an electronic expansion valve driver is fitted alongside the controller. They generally stop the circuit for safety.
| Code | Meaning | What usually causes it | Who can deal with it |
|---|---|---|---|
| Ed1 | Communication error with the driver | The controller has lost contact with the driver for more than a few seconds. Cable, connector or driver fault. The unit is inhibited for safety. | Engineer needed |
| SH1 | Low superheat | Superheat has dropped too low, risking liquid returning to the compressor. The circuit stops after a few seconds. Treat as serious. | F-Gas engineer needed, stop the machine |
| nO1 / LO1 | MOP and LOP warnings | Evaporating pressure above the maximum or below the minimum operating pressure. Display warnings, but they point to load, charge or valve problems. | F-Gas engineer needed |
| HA1 | High inlet temperature warning | Water returning to the evaporator hotter than expected, often after a shutdown. | Usually clears as the system cools |
| ES1 / EP1 / EU1 / Eb1 | Driver probe, EEPROM, valve-open and battery alarms | Driver hardware faults. Eb1 in particular means the driver’s battery back-up cannot guarantee the valve will close on power loss, so compressor start-up is inhibited to prevent liquid return. | Engineer needed |
Because the machine builder sets the parameters, reset behaviour and even which alarms are enabled vary between makes. Treat this as a guide alongside the manual for your specific unit.
Send us a photo of the controller display and the data plate. Our engineers work on process chillers from all major manufacturers, with a 4-hour response target across the West and East Midlands.
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