While warm dust at temperatures about 30K was well detected in normal galaxies by IRAS and the ISO data obtained so far, cold dust at temperatures about 15K was not yet found. Possibly it is too difficult to detect this second dust component within a dust mixture in which the radiation of warm dust dominates. We propose to search for the cold dust component in a normal galaxy by choosing appropriate, spatially resolved regions and applying optimal instrumental configurations. We would like to perform a long scan (AOT P22) right across the southwestern part of the andromeda galaxy M31 using the C200 detector of ISOPHOT with the FIR filters at 120, 135, 180 and 200 micron (centered at 120, 150, 185 and 205 micron). The chosen wavelength regime between 100 and 240 micron is optimal for the investigation of dust at temperatures about 15-30K. It makes full usage of the longer wavelength capabilities of ISOPHOT. The scan hits the ringlike region of relatively warm dust which surrounds the disk. At the same time the scan goes through the inner regions southwest of the bulge with very low 60 and 100 micron radiation, i.e. essentially free of warm dust. The existence of dusty material, however, is indicated for example by Hodge (1980, AJ 85, 376) who found several hundred dark clouds from investigations of photoplates. This inner region seems to be an ideal location to search for cold dust. The colors derived from the ringlike regions allow a direct differential comparison.