Thermo King Alarm 21: Cooling Cycle Check (Zone)
Alarm 21 is listed as 'Cooling Cycle Check (Zone)' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Error Codes
Browse published fault-code records by brand, product and displayed code.
Each record starts with the source meaning, then separates applicability, owner-safe actions, operating uncertainty and qualified-service boundaries. A matching code string alone is not enough: confirm the brand, product, model and controller before acting.
Thermo King Alarm 22: Heating Cycle Check (Zone)
Alarm 22 is listed as 'Heating Cycle Check (Zone)' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 23: Cooling Cycle Fault (Zone)
Alarm 23 is listed as 'Cooling Cycle Fault (Zone)' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 24: Heating Cycle Fault (Zone)
Alarm 24 is listed as 'Heating Cycle Fault (Zone)' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 25: Alternator Check
Alarm 25 is listed as 'Alternator Check' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 26: Check Refrigeration Capacity (Zone)
Alarm 26 is listed as 'Check Refrigeration Capacity (Zone)' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 27: Vapor Motor RPM High (CR)
Alarm 27 is listed as 'Vapor Motor RPM High (CR)' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 28: Pretrip or Self Check Abort
Alarm 28 is listed as 'Pretrip or Self Check Abort' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 29: Defrost Damper Circuit Check (Zone)
Alarm 29 is listed as 'Defrost Damper Circuit Check (Zone)' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 30: Defrost Damper Stuck Closed (Zone)
Alarm 30 is listed as 'Defrost Damper Stuck Closed (Zone)' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 31: Check Oil Pressure Switch
Alarm 31 is listed as 'Check Oil Pressure Switch' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 32: Refrigeration Capacity Low (Zone)
Alarm 32 is listed as 'Refrigeration Capacity Low (Zone)' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 33: Check Engine RPM
Alarm 33 is listed as 'Check Engine RPM' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 34: Check Modulation Circuit
Alarm 34 is listed as 'Check Modulation Circuit' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 35: Check Run Relay Circuit
Alarm 35 is listed as 'Check Run Relay Circuit' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 36: Electric Motor Failed to Run
Alarm 36 is listed as 'Electric Motor Failed to Run' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 37: Check Engine Coolant Level
Alarm 37 is listed as 'Check Engine Coolant Level' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 38: Electric Phase Reversed
Alarm 38 is listed as 'Electric Phase Reversed' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 39: Check Water Valve Circuit
Alarm 39 is listed as 'Check Water Valve Circuit' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 40: Check High Speed Circuit
Alarm 40 is listed as 'Check High Speed Circuit' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 41: Check Engine Coolant Temp
Alarm 41 is listed as 'Check Engine Coolant Temp' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 42: Unit Forced to Low Speed
Alarm 42 is listed as 'Unit Forced to Low Speed' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 43: Unit Forced to Low Speed Modulation
Alarm 43 is listed as 'Unit Forced to Low Speed Modulation' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01Thermo King Alarm 44: Check Fuel System
Alarm 44 is listed as 'Check Fuel System' for Thermo King Truck/Trailer Refrigeration Unit. Verify the exact model and controller before acting.
Source checked 2026-05-01