The definitions of the rank and crank for overpartitions were given by Bringmann, Lovejoy and Osburn. Let N¯(s,l;n)\documentclass[12pt]{minimal}
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\begin{document}$$\overline{N}(s,l;n)$$\end{document} (resp. M¯(s,l;n)\documentclass[12pt]{minimal}
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\begin{document}$$\overline{M}(s,l;n)$$\end{document}, M2¯(s,l;n)\documentclass[12pt]{minimal}
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\begin{document}$$\overline{M2}(s,l;n)$$\end{document}) denote the number of overpartitions of n with rank (resp. the first residual crank, the second residual crank) congruent to s modulo l. The rank differences of overpartitions modulo 3, 5, 6, 7 and 10 were determined. In this paper, we establish the generating functions for N¯(s,l;n)\documentclass[12pt]{minimal}
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\begin{document}$$\overline{N}(s,l;n)$$\end{document}, M¯(s,l;n)\documentclass[12pt]{minimal}
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\begin{document}$$\overline{M}(s,l;n)$$\end{document} and M2¯(s,l;n)\documentclass[12pt]{minimal}
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\begin{document}$$\overline{M2}(s,l;n)$$\end{document} with l=4,8\documentclass[12pt]{minimal}
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\begin{document}$$l=4, 8$$\end{document} by utilizing Appell–Lerch sums and theta function identities. Moreover, in light of these generating functions, we obtain some equalities and inequalities on ranks and cranks of overpartitions modulo 4 and 8.