Measurements of the transmission and reflection spectra of a CdSiP2 single crystal, performed in the temperature range from 80 to 300 K using pulsed terahertz and infrared Fourier spectroscopy, revealed a significant impact of post-growth defects on absorption in the THz range. It was found that this absorption is weakly dependent on temperature, in contrast to the previously obtained results for another crystal of the chalcopyrite family with s significantly lower concentration of defects. When cooling, the intrinsic absorption mechanisms were minimized and the contribution of defects to absorption was extracted