Over the past 12 years we have been conducting a survey of IRAS (PSC) sources with dust temperatures between 100 and 250 K, which is the temperature of AGB shells after mass loss has ceased. About 1000 PSC sources fulfill this criterion, about half of them identified previously in the literature: most are PNe (49%) and post-AGB stars (27%), but there is also a small fraction of young stellar objects and active galaxies. In order to classify the unidentified sources, we took low resolution spectra of these objects, in the range from 3500 to 9000 Å. The region between 3600 and 5050 Å has been used to carry out the spectral classification of most of the unidentified sources. Partial results are presented here: of the 187 objects studied, 34 were PNe, 10 proto-PNe and 103 post-AGB candidates with or without Hα emission. The rest have been identified as young stellar objects (34), LBVs (2), and active galaxies (3).