Mercedes Benz repair: Mercedes repair, gasoline station, mercedes repair

Question
On my E300 1993, gasoline station wagon the heater/defroster/cooling fan has gotten slower and slower until hardly any air flows. The fuse and the switch are ok Is this replaceable. Can I do it myself? I have experience repairing other cars. Thanks  Bob

Answer
either your duovalve is shot or the hose going to the valve is shot.jack up car and take off front passenger wheel well you will se a grey tube with a plastic check valve there follow the grey tube chances are it snapped otherwise take out the 4 screws that hold your duovalve on and check to see if your plungers are still intact make sure to unplug it first