The bimodal random crystal field (D) effects are investigated on the phase diagrams of spin-3/2 Ising model by using the effective-field theory with correlations based on two approximations: the general van der Waerden identity and the approximated van der Waerden identity. In our approach, the crystal field is either turned on or turned off randomly for a given probability p or q - 1 - p, respectively. Then the phase diagrams are constructed on the (Delta, kT/J) and (p, kT/J) planes for given p and Delta, respectively, when the coordination number is z = 3. Furthermore, the effect of randomization of the crystal field is illustrated on the (Delta, kT/J) plane for p = 0.5 when z = 3, 4, and 6. All these are carried out for both approximations and then the results are compared to point out the differences. In addition to the lines of second-order phase transitions, the model also exhibits first-order phase transitions and the lines of which terminate at the isolated critical points for high p values.