Thermodielectric effect in dual-frequency cholesteric liquid crystals (DFCLCs) is an important issue and has rarely been studied in the past. DFCLC materials have many applications such as fast-switching CLCs, light modulators, and tunable photonic devices. However, DFCLCs characteristically need high operation voltage, which hinders their further development in thin-film-transistor operation. Here we present a lower-voltage switching method based on thermodielectric effect. Dielectric heating effect entails applying an electromagnetic wave to occasion dielectric oscillation heating so to induce the increase in crossover frequency. The subsequent change in dielectric anisotropy of the DFCLC permits the switching, with a lower voltage, from the planar state to the focal conic or homeotropic state. Furthermore, we also demonstrate the local deformation of the CLC helical structure achieved by means of the thermodielectric effect. The wavelength of the deformation-induced defect mode can be tuned upon varying the dielectric heating power. The physics and the calculation of dielectric heating in DFCLCs are described.