The Thermo King Thermoguard 6 5D44022G24 is a microprocessor‑based temperature controller used in commercial refrigerated transport units to regulate compressor, fan, and coolant flow for precise cargo temperature management. Common failure modes include loss of communication with the refrigeration unit (often due to faulty wiring or degraded connectors), power supply voltage drops or spikes causing the controller to reset, and internal component degradation such as blown fuses or failed relays that interrupt cooling cycles. For initial troubleshooting, verify 24 V DC input stability, inspect all I/O connections for corrosion or loose terminals, and review any diagnostic error codes displayed on the panel; if no code appears, perform a visual inspection of the PCB for burn marks or damaged components before proceeding to component‑level testing.[oss-gpt-20b]