Responded to service call for a Samsung mini-split heat pump (approximately 1.5 years old) exhibiting intermittent C4 error codes and no heat operation. Upon testing, unit immediately entered defrost mode when temperature was increased. Consulted with technical support and performed diagnostic testing on temperature sensors, finding multiple sensors operating outside of specification parameters. Identified potential control board failure. Will return with replacement temperature sensors, wiring harness, and control board. If issues persist after component replacement, refrigerant charge will be evaluated.
