Chiller Fault Codes
Centrifugal and screw liquid chiller diagnostics for Trane, Carrier, York / Johnson Controls, Daikin Applied, Climacool, and Multistack.
Reversed phase sequence detected on incoming power at compressor startup — must trip within 0.3 s.
- Power supply wiring phased incorrectly
- Utility power reversal after outage
- Starter contactor wired out of sequence
- Verify incoming phase sequence with a phase rotation meter
- Check all power wiring connections at the starter terminals
- Inspect for recent utility work or power restoration events
One or two phases of compressor current lost while running or starting; trip at <10% RLA for 2.64 s.
- Blown fuse on one phase
- Open contactor contact
- Loose power terminal
- Utility single-phasing
- Check all three fuses at the motor disconnect
- Verify current on all three phases with a clamp meter
- Inspect contactor contacts for burning or pitting
- Tighten all power terminal connections
Loss of power for three or more line cycles detected (MPL option must be enabled). Auto-resets in 30 s.
- Utility voltage sag or brief outage
- Loose incoming power connection
- Overloaded electrical distribution
- Check utility voltage logs or power quality meter
- Inspect incoming connection tightness
- Review chiller event history for frequency of occurrence
All three phases of compressor current lost while running (previously established). Auto-resets in 10 s.
- Complete power interruption
- Utility outage
- Main breaker trip
- Confirm utility power restoration
- Reset main breaker if tripped
- Check for nuisance MPL if recurring
30% current imbalance on one phase relative to 3-phase average sustained for 90 continuous seconds.
- Unbalanced utility supply voltage
- Single weak contactor contact
- Motor winding beginning to fail
- Measure and compare all three line voltages
- Check contactors for wear
- Log all three phase currents during run
- Notify utility if supply imbalance exceeds 2%
Current detected on CTs when only the 1M (1K1) main contactor is closed at start — indicates shorted secondary contactor. Y-delta starters only.
- Shorted run contactor
- Wiring fault between contactors
- Inspect all starter contactors for welded contacts
- Verify wiring per starter schematic
Current detected on CTs when only shorting contactor (1K3) is energized — indicates shorted 1M contactor.
- Welded main contactor (1M/1K1)
- Wiring cross-fault
- Check 1M contactor for welded tips
- Inspect wiring for shorts
No CT current 1.6 s after both shorting and main contactors energized — motor not responding to start command.
- Open motor winding
- Blown fuse after contactor
- Motor terminal disconnect loose
- Verify power at motor terminals under load
- Meg-ohm test motor windings
- Check post-contactor fusing
Solid State Starter (SSS) fault relay opened — internal SSS protection activated.
- SSS internal overload
- SCR device failure
- Communication fault between SSS and UC800
- Read SSS local fault display or LED indicators
- Check SSS-to-UC800 signal wiring
- Verify SSS power supply
Adaptive Frequency Drive (AFD) fault relay opened — internal VFD protection triggered.
- VFD internal fault (overcurrent, overvoltage, overtemperature)
- VFD-to-UC800 communication loss
- Drive cooling fan failure
- Read drive keypad fault code
- Check drive cooling airflow and filter
- Verify DC bus voltage within spec
- Check drive-to-controller communication cable
Transition-complete signal not received within 2.5 s of transition command. Y-delta, autotransformer, primary reactor, X-line starters.
- Run contactor failed to close
- Transition complete limit switch malfunction
- Wiring fault on transition signal circuit
- Check transition complete wiring to UC800
- Manually test run contactor operation
- Verify contactor auxiliary contact continuity
SSS did not signal Up to Speed or End of Ramp within 2.5 s after commanding bypass — applies to SSS/AFD only.
- Excessive load at startup
- Motor shaft binding or mechanical restriction
- SSS ramp rate set too slow
- Check compressor for mechanical binding
- Verify SSS acceleration time setpoint
- Inspect motor for high temperature (recent overload)
Motor did not reach <85% RLA within maximum acceleration timer — start aborted.
- Motor overloaded
- Low supply voltage during start
- Mechanical restriction in compressor
- Check supply voltage under load
- Verify maximum acceleration timer setting
- Inspect compressor for mechanical resistance
Transition complete input shorted before compressor start — wiring fault.
- Wiring short circuit on TC input
- Defective auxiliary contact reporting closure
- Inspect wiring for short to ground or common
- Test auxiliary contact with ohmmeter
At Speed input shorted before compressor start (SSS/AFD). Indicates wiring fault.
- Wiring short on At Speed signal
- Defective SSS or AFD feedback contact
- Test At Speed feedback wiring for shorts
- Verify SSS/AFD output contact
Transition complete input opened while compressor running — contactor auxiliary contact dropped out.
- Run contactor dropped out unexpectedly
- Auxiliary contact worn or intermittent
- Loose wiring on TC input
- Check run contactor for premature dropout
- Test auxiliary contact under running conditions
- Inspect terminal tightness
At Speed input opened while compressor running (SSS/AFD) after successful bypass.
- SSS or AFD At Speed output dropped mid-run
- Intermittent wiring on At Speed signal
- Monitor SSS/AFD At Speed output during run
- Check wiring and connections
Compressor current exceeded overload trip characteristic (must trip = 140% RLA, nominal trip at 132.5% in 30 s).
- Overloaded compressor from high differential pressure
- Low supply voltage causing higher current draw
- Motor bearing failure
- Refrigerant overcharge
- Check condenser approach temperature and condenser water flow
- Verify supply voltage at full load
- Compare actual current to RLA nameplate
- Check refrigerant charge
Compressor current >10% RLA detected on any phase when compressor commanded off — contactor failed to open.
- Welded main contactor contacts
- Shorted SCR in SSS
- Immediately check contactor for welded tips
- Lock out and tag out — do not restart
- Inspect SSS for shorted SCR
Average line voltage exceeded +10% of nominal (nominal trip: 60 s at >112.5%). Auto-resets at 109% or less.
- Utility overvoltage condition
- Failed voltage regulator on transformer
- Tap setting on transformer too high
- Measure supply voltage at all three phases
- Check transformer tap setting
- Contact utility if voltage consistently high
Average line voltage below -10% of nominal (nominal trip: 60 s at <87.5%). Auto-resets at 90% or greater.
- Utility undervoltage
- Overloaded electrical panel
- Loose main feed connection
- Transformer tap set too low
- Measure supply voltage under full load
- Check transformer tap setting
- Inspect main feed terminals for heat or looseness
- Contact utility
Saturated evaporator refrigerant temperature (from suction pressure) dropped below Low Refrigerant Temperature Cutout (LRTC) setpoint for a 450°F-s integral.
- Loss of chilled water flow
- Low load with LRTC setpoint too high
- Refrigerant undercharge
- Fouled evaporator tubes
- Verify evaporator water flow and differential pressure
- Check chilled water pump operation
- Confirm refrigerant charge
- Check LRTC setpoint (min -5°F)
Oil pressure ratio (PC-Po)/(PC-PE) out of acceptable range for 15 s while differential pressure >15 psiD.
- Oil pump failure
- Clogged oil filter
- Low oil level
- Oil cooler blockage
- Check oil differential pressure on service tool
- Inspect oil filter condition
- Verify oil level in sight glass
- Check oil cooler for fouling
Oil loss level sensor detects lack of oil in the oil tank while compressor is running.
- Oil pump failure
- Oil return line blockage
- Low refrigerant charge causing oil migration
- Eductor system not functioning
- Check oil level and sight glass while running
- Inspect oil pump operation
- Verify eductor operation
- Check for refrigerant undercharge
Oil loss level sensor detects lack of oil 90 s after EXV preposition completed during pre-start. Start delayed.
- Insufficient oil in system
- Oil migration during off-cycle
- Oil pump not priming
- Verify oil level at pre-start
- Add oil if below minimum
- Check heater operation during off-cycle
System differential pressure (condenser-evaporator) below 15 psiD for >164 psiD-s, or below 23 psiD for >3000 psiD-s (non-volatile integral).
- Refrigerant leak
- EXV stuck open flooding evaporator
- Low load condition
- Compressor valve failure
- Verify differential pressure on service tool
- Check refrigerant charge
- Inspect EXV operation
- Check for refrigerant leaks
System differential pressure below 7.7 psiD — saturates the Low Diff Rfgt Press integral and invokes compressor cool-down mode.
- Major refrigerant leak
- Flooded evaporator
- Compressor not building head pressure
- Check for major refrigerant leak immediately
- Inspect compressor operation
- Verify condenser water flow
BAS was configured as 'installed' at MP and Comm 3 LLID lost communications with BAS for 15 continuous minutes.
- BACnet/Modbus network cable fault
- BAS controller offline
- Communication module (LLID) failure
- Incorrect address or baud rate
- Check BAS network wiring and terminations
- Verify BAS controller is online
- Confirm Comm 3 LLID LED status
- Verify communication parameters match BAS
AFD on compressor 1A reports motor current overload condition.
- High differential pressure overloading compressor
- Low supply voltage
- Drive parameter mismatch
- Check condenser pressure and approach
- Verify drive motor nameplate parameters
- Check supply voltage
AFD on compressor 2A reports motor current overload — same criteria as code 504 for circuit 2.
- High differential pressure on circuit 2
- Low voltage
- Mechanical restriction on compressor 2A
- Check circuit 2 condenser pressure
- Verify drive parameters for ckt 2
- Inspect compressor 2A for binding
AFD interrupt signal failure on compressor 1A — internal drive communication failure.
- Drive control board failure
- Noise on drive communication bus
- Drive firmware issue
- Power-cycle the drive after lockout
- Check drive for internal fault codes
- Inspect drive control wiring for noise sources
Main processor successfully came out of reset and rebuilt application (power-up, software install, or reconfiguration). Informational — auto-clears.
- Normal power-up
- Software update applied
- Watchdog-triggered reset
- Review historic diagnostic list for prior faults that caused reset
- Confirm no other active diagnostics
Starter module reported stopped when it should be running, and no starter diagnostic exists. Auto-logs and clears.
- Power transient caused brief starter dropout
- Starter communication glitch
- Loose starter signal wiring
- Review event history for frequency
- Check starter signal wiring
- Monitor supply voltage quality
Leaving chilled water temperature dropped below the Low Chilled Water Temperature Cutout setpoint (typically 36–40°F for water; lower for glycol). Non-latching auto-reset.
- Low chilled water flow
- Load turned off suddenly
- Control setpoint set too close to low limit
- Freeze protection activation
- Verify chilled water pump is running and flow is established
- Check LWCO setpoint vs. system requirements
- Inspect for glycol concentration if applicable
Condenser refrigerant pressure exceeded condenser pressure cutout setpoint (adaptive — typically 132 psiA for R-134a). Compressor unloads, then trips if not recovered.
- Insufficient condenser water flow
- High condenser water entering temperature
- Non-condensables in refrigerant
- Fouled condenser tubes
- Verify condenser water flow and pump operation
- Check cooling tower performance
- Review condenser approach temperature
- Check for non-condensables — purge unit if equipped
Chiller surge detected; adaptive control is unloading compressor to prevent continued surge. Operating mode displayed as 'Surge'.
- Low load condition forcing compressor to minimum capacity
- High condenser / low evaporator pressure differential
- IGV calibration out of spec
- Hot gas bypass failure
- Check system load — chiller may be oversized for current conditions
- Verify IGV position and calibration
- Confirm hot gas bypass (if installed) is operating
- Review compressor differential pressure
Evaporator water flow not proven within 20 minutes of pump start command (4 min 15 s if pump override). Non-latching; clears when flow returns.
- Evaporator pump failure
- Closed isolation valve
- Flow switch or differential pressure switch failed
- Air pocket in chilled water loop
- Verify pump is running (check amps)
- Check flow switch or DP switch
- Open all isolation valves
- Bleed air from system
Condenser water flow not proven within the configured wait period. Non-latching; clears when flow returns.
- Condenser pump failure
- Closed condenser isolation valve
- Cooling tower pump interlock not met
- Flow switch malfunction
- Verify condenser pump is running
- Check all condenser isolation valves
- Test condenser flow switch
- Verify cooling tower pump interlock
Motor winding temperature exceeds the inhibit setpoint — chiller start blocked until temperature recovers.
- Recent trip from overload
- Failed motor temperature sensor
- Inadequate motor cooling (refrigerant)
- Allow adequate cooling time before restart
- Check motor temperature sensor wiring and calibration
- Verify motor refrigerant cooling circuit is open
Suction (evaporator) pressure exceeded the high suction pressure limit — compressor may be operating in a flooded condition.
- EXV stuck open
- High load condition
- Refrigerant overcharge
- Check EXV operation and control signal
- Monitor entering chilled water temperature
- Review refrigerant charge
Anti-short-cycle timer preventing immediate restart after shutdown. Non-latching; auto-clears when timer expires.
- Recent shutdown — normal protection
- Chiller cycling on minor alarms
- Allow timer to expire (typically 3–5 minutes)
- Review cause of preceding shutdown
Oil pressure not established during prelube period before compressor start.
- Oil pump failure
- Clogged oil strainer/filter
- Low oil level in sump
- Oil heater not maintaining temperature (viscous oil)
- Verify oil pump operation
- Check oil filter differential pressure
- Verify oil level and temperature
- Check oil heater energization during off-cycle
Phase current imbalance detected, causing capacity limit mode. Chiller continues to run but capacity is reduced.
- Unbalanced utility supply
- Partial single-phase condition
- Motor winding degradation
- Measure all three phase voltages
- Check three-phase motor current balance
- Notify utility if voltage imbalance
Communication to the Tracer building automation controller has been lost.
- Network cable disconnected or damaged
- Tracer controller offline or rebooting
- Incorrect address or baud settings
- LLID communication module failure
- Check Tracer communication cable connections
- Verify Tracer controller is online
- Confirm LLID for Tracer comm shows green LED
- Verify baud rate and address match
Oil sump pressure is below the high-vacuum inhibit threshold — chiller start blocked to protect compressor seals.
- Non-condensables or refrigerant leak creating vacuum condition
- Refrigerant undercharge
- Chiller idle in cold ambient
- Check system refrigerant pressure
- Inspect for leaks
- Warm chiller before starting in cold ambient
- Check purge unit operation if applicable
Oil temperature too low to permit safe start — typically <100°F. Oil heater must warm oil first.
- Oil heater failure or not energized
- Long idle period in cold ambient
- High refrigerant concentration in oil
- Verify oil heater is energized and functioning
- Check oil temperature on display
- Inspect oil heater wiring and element continuity
Purge unit running excessively, indicating non-condensable buildup or refrigerant leak.
- Air ingress through leaking valve packing
- Refrigerant leak allowing air entry during vacuum
- Purge unit malfunction
- Perform leak check on entire refrigerant circuit
- Check purge regeneration rate
- Test purge unit operation
Compressor current has reached the active current limit setpoint — chiller is running but loading is inhibited.
- Demand limit commanded from BAS or external signal
- High differential pressure limiting capacity
- Low supply voltage increasing current
- Check active current limit setpoint source (BAS, external, panel)
- Monitor condenser and evaporator conditions
- Verify supply voltage
Building automation system has commanded a run inhibit on the chiller.
- Demand shed from BAS
- Scheduled off command
- Safety interlock from BAS-side logic
- Check BAS schedule and setpoints
- Verify no demand shed active
- Review BAS logic for inhibit conditions
Adaptive Frequency Drive (variable speed centrifugal) has an active fault. Drive alarm message simultaneously displayed on AdaptiView.
- Drive overcurrent or overtemperature
- Drive cooling failure
- Input power disturbance
- Motor insulation fault
- Read drive fault code on Tracer AdaptiView display
- Inspect drive cooling fan and filter
- Check DC bus voltage
- Perform insulation resistance test on motor