Compressor Problems
84 related codes
Compressor not starting, short cycling, overheating, low oil pressure or contactor failure. Codes that point to compressor lockout or protection trips.
Low Refrigerant Level
Lack of refrigerant in the system's refrigeration circuit.
Check/Low Engine Oil Pressure
Engine oil pressure is dangerously low, triggering unit shutdown.
High Discharge Pressure
Refrigerant discharge pressure exceeded the safety limit.
High A/C Amps
High electrical current detected in AC system components.
Alarm 17 – High Compressor Discharge Temperature (CDT)
Carrier Transicold alarm code 17 (AL17) triggers when Compressor Discharge Temperature (CDT) climbs above the safety threshold — typically 310°F (154°C) on Vector, X4, X2 and Supra reefer units. The Advance controller shuts the unit down to protect the compressor from thermal breakdown of oil, valve plate damage, and burned windings. AL17 almost always points at a refrigerant-side or airflow problem, not the compressor itself.
Maximum Compr Alarms
Maximum number of consecutive compressor alarms reached.
Low Suction Superheat
Low suction superheat, risk of liquid floodback to compressor.
A/C Current Over Limit
AC current consumption exceeded pre-set limits.
Compression Ratio Exceeded
Pressure ratio between suction and discharge out of range.
High Suction Pressure
Suction pressure higher than allowed limit for the engine.
Check Refrig System
The system detected poor cooling efficiency.
Failed To Run Min Time
The engine stopped before reaching minimum warm-up time.
Compressor Motor Overload
The compressor motor overload relay has tripped due to excessive current.
Check UL1 Circuit
Electrical failure detected in the Compressor Unloader 1 (UL1) circuit.
Check UL2 Circuit
Electrical failure detected in the Compressor Unloader 2 (UL2) circuit.
Check Comp Contactor 1
Error in compressor contactor 1.
Overload/Ground Fault
Electrical overload or ground fault detected in the system.
Check Comp Discharge Sensor
An abnormal reading is detected at the compressor discharge temperature sensor.
Check Clutch Circuit
Compressor clutch circuit failure detected during Pretrip.
Check Disch Temp Sensor
Compressor discharge temperature sensor out of range.
Check Suction Temp Sensor
Compressor suction temperature sensor is not responding correctly.
Can Not Pump Down
The system failed to perform internal vacuum (Pump Down) within the established time.
Check Bypass
Generic or flow failure in the bypass valve detected by pressure sensors.
Check LIV
Flow or mechanical failure in the Liquid Injection Valve (LIV).
High Suction Pressure
Excessively high suction pressure detected during diagnostic tests.
Low Suction Pressure
Suction pressure below the permitted operating limits.
High Discharge Pressure
Dangerously high discharge pressure; risk of high pressure cutout.
Check Clutch
Failure in the coupling or electromagnetic clutch of the compressor.
Low Discharge Pressure
Insufficient discharge pressure; the unit cannot compress effectively.
High Side Leak
Presumptive detection of a leak in the high-pressure side of the system.
Low Suction Pressure
Critical low suction pressure detected by the transducer.
Check Comp Contact Circuit
Failure detected in the compressor contactor circuit (electric/standby mode).
Dis Press Calibrate Error
Calibration failure of the discharge pressure sensor; data is out of range.
Low Discharge Superheat
Low discharge superheat detected; risk of liquid floodback to the compressor.
Check Clutch Slip
Detection of clutch slip; loss of power transfer.
No Setpoint Change
An attempt to change the setpoint was made but could not be validated in the main zone.
Check Clutch Circuit
Error detected in the compressor clutch circuit.
Suction Pressure Sensor
Fault in the suction pressure sensor of the refrigeration system.
C2 Chk Evap1 Superheat
Superheat out of range in evaporator 1 of compartment 2.
Oil Pressure Error ENCU
Error detected in the engine oil pressure signal.
High Discharge Pressure (or Temperature)
The compressor discharge pressure or temperature has exceeded safety limits.
Low Engine Oil Pressure
The engine oil pressure is dangerously low.
Cooling Cycle Check (Zone)
The system detects insufficient cooling capacity during monitoring.
Cooling Cycle Fault (Zone)
Critical system failure preventing cooling; unit shuts down to protect cargo.
Check Refrigeration Capacity (Zone)
Refrigeration capacity is lower than expected for the current setpoint.
Vapor Motor RPM High (CR)
Steam motor or electric compressor revolutions exceed the safety limit.
Check Oil Pressure Switch
The microprocessor detected a discrepancy between actual oil pressure and the pressure switch status.
Refrigeration Capacity Low (Zone)
The unit or zone is not reaching the expected cooling capacity and has been stopped for safety.
Unit Forced to Low Speed Modulation
The unit is forced to low speed due to a limitation in the modulation system.
Check Belts or Clutch
A mechanical issue has been detected in the drive belts or the clutch.
Check Compressor Temp Sensor
Compressor temperature sensor circuit is out of range or faulty.
High Compressor Temp
The compressor temperature is unusually high, approaching the safety limit.
High Compressor Temp Shutdown
The unit stopped to protect the compressor due to excessive temperature.
Check Discharge Pressure Sensor
The controller detected an erroneous signal from the discharge pressure sensor.
Check Suction Pressure Sensor
The controller detected an erroneous signal from the suction pressure sensor.
ETV Fault – Electronic Throttling Valve Circuit (Code 89)
Thermo King alarm code 89 indicates a failure in the Electronic Throttling Valve (ETV) control circuit. The ETV is a stepper-motor modulating valve in the suction line that regulates suction pressure and compressor loading on Thermo King SB-, SLXi, SLXe, SLX, SLX Whisper, T-Series, Precedent and TriPac reefer units. When the microprocessor cannot drive or read the ETV stepper coils correctly, it logs Code 89 and forces the unit into a protective mode — often unable to hold setpoint or pull down.
Low Compressor Suction Pressure
Dangerously low compressor suction pressure detected.
Check Loader #1 Circuit
Fault in the compressor loader/unloader #1 circuit.
Check Loader #2 Circuit
Fault in the compressor loader/unloader #2 circuit.
High Compressor Pressure Ratio
Excessive pressure ratio detected between compressor suction and discharge, risking mechanical integrity.
Check High Discharge Pressure Sensor
Error in the high discharge pressure sensor (Replaced by code 86 in newer models).
Check High Pressure Cut Out Switch
Fault in the High Pressure Cut Out (HPCO) switch or its circuit.
Check PMW Liquid Injection Circuit
Failure in the Pulse Width Modulation (PMW) liquid injection circuit, crucial for compressor cooling.
Check Back Pressure Regulator (CR)
Indicates a problem with the suction pressure regulator or back pressure regulator, affecting temperature stability.
Low Suction Pressure Switch Failure
Inconsistent state or failure detected in the low suction pressure switch.
TriPac Compressor Alarm
A generic alarm condition has been detected in the TriPac compressor system.
Check Digital Scroll Output Circuit (Scroll Only)
A fault has been detected in the digital scroll compressor output control circuit.
High Compressor Suction Pressure (Scroll Only)
Excessively high suction pressure detected in Scroll-type compressors.
Low Compressor Suction Ratio (Scroll Only)
Suction pressure ratio below safe operating limits for the Scroll compressor.
Low Compressor Discharge Pressure (Scroll Only)
Scroll compressor discharge pressure too low during operation.
Minimum ETV Discharge Superheat Temp (Scroll)
ETV controlled discharge superheat is at the minimum thermal limit.
Low Pressure Differential (Scroll only)
Low differential pressure detected across the compressor (Scroll only).
ECU Forced Low Speed
The Engine Control Unit (ECU) has forced the engine to low speed to protect the system due to an out-of-range operating condition.
High Temperature Alarm
Temperature above the configured limit.
High Discharge Pressure
High pressure switch opened due to overpressure.
Low Suction Pressure
Low pressure switch activated.
Compressor Thermal Protector Open
Protection module detected compressor overheating.
High Discharge Pressure (HP)
High pressure switch activated on Bitzer compressor.
Low Suction Pressure (LP)
Low pressure switch activated.
High Discharge Gas Temperature
PTC sensor in compressor head exceeded 140°C.
Oil Differential Pressure Failure
Delta P-MP10 detected low oil pressure for >90 seconds.
Electric Standby Overload (DSR)
Electric standby motor drew excessive current and tripped the overload protection.
High Discharge Pressure (DSR)
Discharge pressure exceeded safe operating limit and shut down the unit.
Low Suction Pressure (DSR)
Suction pressure dropped below the minimum allowed value.