Adaptive code modulation (ACM) has been studied for last two decades to enhance the bandwidth and power efficiency in a bandwidth-constrained and power-constrained communication system environment. This paper studies how to decide the boundaries of a signal-to-noise ratio (SNR) for the ACM mode selection for a given set of parameters and system model. Also, this paper proposes an efficient and practical algorithm to search the proper ACM mode that meets a target bit error rate (BER) and achieves the maximum data rate. The proposed algorithm is found to be effective under jamming and interference, even if channel and jamming state information (JSI) are unavailable. The results in this paper can be applicable for future satellite and mobile communication system designs against jamming and interference environments.