Do a search on 124 a/c diagnostics or some such to find out how to use an LED to draw climate control trouble codes from the connector near the battery. If there is a bad sensor in the system, the trouble code will tell you which one.

Also, cut a 1cm square of paper and put it against the little grille near the rearview mirror. With the ignition key on the paper should be held against the grille. If not find and check the sample blower fan. On my car it is to the right of the glove box. It has been in several different locations throughout the 124 series.

Good luck,