Ptolemy's models for the planetary motion required a special place for the Sun. In a purely geocentric model there would be no reason that the motion of the Sun and the planets should be correlated. This material is explained in Crowe's book, p. 49, "Theories of the World from Antiquity to the Copernican Revolution(2nd revised edition)".
 
 

Exercise: 1) On a separate sheet of paper draw two circles around the sun and mark the position of the earth, e,  and an outer planet p. 2) Draw the deferent of radius rp around the earth. 3) The planet is a distance re away from the center c of the epicycle. Draw a circle of radius re around p. 4) Where the epicycle circle intersects the deferent is the location of c. 5) Draw in the lines se, sp, rp, pc. You should see a parallelogram.