Carrier Pro-Dialog Plus Alarm Codes Explained

Which Chillers This Covers

Pro-Dialog Plus is the control system on Carrier 30GX air-cooled and 30HXC water-cooled screw chillers. These are large machines, typically on process, data centre or district cooling duty, so an alarm usually means a significant load has stopped.

Carrier’s smaller air-cooled ranges use different control platforms, so if your unit is not a 30GX or 30HXC, check the code style against this page before relying on it. Not sure? Send a photo of the display and the data plate to info@evolution-cooling.com or call 0121 820 8946 and we will tell you.

Reading and Resetting Alarms

The alarm LEDs give the quickest read on the state of the machine:

• Flashing LED: the circuit is still running, but there is an alarm.
• Steady LED: the circuit has shut down on a fault.

The Alarm menu shows up to five active codes. To reset manually, hold the MENU button until the Alarms LED lights, press the button to authorise the reset, then press again to confirm. The display shows “Good”, then the alarm count, then 0 AL.

Two things worth knowing. Alarms can be reset while the unit is running, so you do not have to stop the machine to clear one, which also makes it easy to clear something that should have been investigated. And after a power interruption the unit restarts automatically, but faults that were active when the power went are saved and can stop a circuit restarting.

Sensor and Transducer Faults (1 to 28)

These are nearly always a failed sensor, a damaged cable or a wiring fault, and almost all reset automatically once the reading returns to range. What they shut down varies.

Code	Meaning	Effect
1 / 2	Evaporator entering and leaving fluid thermistor failure	Unit shuts down
3 / 4	Condenser entering and leaving fluid thermistor failure	Message only in cooling; shuts down in heating
5 / 6	Heat reclaim condenser thermistor failures	Message only
7 / 8	Discharge gas thermistor failure, circuits A and B	That circuit shuts down. Can also indicate genuinely high discharge temperature
9 to 12	Motor sensor faults, compressors A1, A2, B1, B2	That compressor shuts down
13	External 0-10V signal fault	Demand limit deactivated
14 to 17	Discharge and suction pressure transducer failures	That circuit shuts down
18 to 21	Oil pressure transducer failures, per compressor	That compressor shuts down
22 to 25	Economiser transducer failures	Circuit or compressor shuts down depending on configuration
26	Transducer supply defective	Unit shuts down. Board failure or wiring
27 / 28	Evaporator liquid level sensor failure	Circuit keeps running, but the expansion valve reverts to superheat control

Who can deal with these: engineer. They are diagnostic rather than mechanical, but they need someone with the right meter and access to the boards.

Communication Faults (29 to 43)

Pro-Dialog Plus is a networked control system, and these codes mean one board has stopped answering. Causes are bus wiring faults, an incorrect address or a failed board.

• 29 to 32: loss of communication with a CPM compressor board. That compressor stops.
• 33 to 36: loss of communication with a 4xDO board. A circuit or compressor stops.
• 37 / 38: loss of communication with an expansion valve board. That circuit stops.
• 39 / 40: loss of communication with a fan board.
• 41 to 43: loss of communication with an analogue board. Effect depends on options fitted.

Who can deal with these: engineer. Worth noting that a batch of communication alarms appearing together usually points to a supply or bus problem rather than several failed boards.

Refrigeration and Oil Faults (44 to 71)

These are the ones that matter most, because they are the machine protecting itself.

Code	Meaning	What usually causes it	Who can deal with it
44 / 45	Discharge pressure too high, circuits A and B	Defective transducer or high pressure switch, a fan circuit fault, restricted condenser water flow, or condenser entering water or air temperature too high. Resets automatically within the following ten minutes, so a machine that keeps losing capacity in hot weather may be doing this repeatedly without anyone noticing.	Site team can check the coil, fans and condenser water. Engineer for the rest
46 to 49	Oil solenoid failure, per compressor	Oil valve defective. The compressor is not allowed to start. Manual reset.	Engineer needed
50 to 53	Pre-start oil pressure, per compressor	The oil pump has not built enough pressure before start. The compressor cannot start. Manual reset.	Engineer needed
54 / 55	Low oil level, circuits A and B	Oil level control contact open. The circuit shuts down. Often oil logging in the system rather than simply low oil.	Engineer needed
56 / 57	Low saturated suction temperature	Usually refrigerant loss, restricted flow or an expansion valve problem. The circuit shuts down.	F-Gas engineer needed
58 / 59	High saturated suction temperature	Detected after 90 seconds of operation. Often load well above design, or a control problem.	Engineer needed
60 / 61	Low discharge superheat	Superheat below 2.8 K for ten minutes, which risks liquid returning to the compressor. Circuit shuts down. Treat as serious.	F-Gas engineer needed, do not reset and run
62 to 65	Maximum oil pressure difference, per compressor	The difference between discharge and oil pressure is too great, typically a blocked oil filter. Compressor shuts down.	Engineer needed
66 / 67	Loss of communication with System Manager, or with the master or slave unit	Network fault. The unit returns to autonomous operation rather than stopping.	Engineer needed, but production continues
68 to 71	Low oil pressure, per compressor	Oil pressure differential below the minimum. The compressor shuts down. This is a compressor-saving alarm.	Engineer needed, stop the machine

Frost Protection, Water Flow and Heat Reclaim (72 to 84)

Code	Meaning	What usually causes it	Who can deal with it
72	Evaporator frost protection	Entering or leaving water temperature approaching freezing. The unit shuts down and the evaporator pump is started. Low flow, weak glycol or a setpoint too close to freezing. See our glycol concentration guide.	Site team can check flow and glycol. Engineer if it repeats
73 / 74	Condenser frost protection, circuits A and B	Water-cooled units. The unit shuts down and the condenser pump starts.	Engineer needed
75	Evaporator water flow control failure	The flow switch has not proved flow. Blocked strainer, closed valve, airlocked or failing pump. Unit shuts down. Manual reset.	Site team can check strainer, valves and pump
76	Condenser water flow loss	Same on the condenser side of a water-cooled unit, or a thermostat box fault.	Site team can check the condenser circuit
77	Unit emergency stop	An emergency stop command received over the CCN network. Not a mechanical fault.	Check with whoever issued it
82 to 84	Heat reclaim faults	Communication loss with the heat reclaim board, or a heat reclaim interlock or flow fault on circuit A or B. The circuit stays in cooling mode.	Engineer needed

CPM Compressor Protection Codes (01 to 17)

These two-digit codes come from the CPM modules that protect each compressor motor, and they are nearly all electrical. If you are seeing these, the compressor is being protected from the supply or from itself, and resetting without investigating is how expensive mistakes happen.

Code	Meaning
01	High pressure switch tripped
02	No motor current detected
03 / 04	Current imbalance above 10% and above 18%
05	Current drop in one phase
06	High motor current
07	Ground current fault
08 / 09	Voltage imbalance above 3% and above 7%
11	Voltage phase reversal. The compressor will not start
12	Contactor failure. Unit shuts down
13	Current phase reversal
14	High motor temperature
15 / 17	Motor thermistor open circuit, or short circuited
16	Configuration block fault

Who can deal with these: engineer, working with your site electrician where the fault is on the supply. Phase reversal and voltage imbalance codes often follow electrical work or a supply event, and are the site’s problem rather than the chiller’s.

Which Carrier Alarms Are Safe to Reset?

• Usually safe once you have checked the cause: 75 and 76 water flow, after checking strainers, valves and pumps.
• Reset once, then stop: 44 and 45 high discharge pressure, 72 evaporator frost protection.
• Do not simply reset: anything oil related (46 to 55, 62 to 71) and 60 or 61 low discharge superheat. These protect a screw compressor, which is the most expensive component on the machine by a wide margin.
• Investigate before resetting: all CPM codes. They point at the electrical supply or the motor.

Codes and behaviour vary with machine configuration and software version, so treat this as a guide alongside the manual for your unit. We maintain and repair Carrier chillers alongside all other major makes across the Midlands.