Heating and Air conditioner on 2000 Mercedes-Benz S430

The heater and or Air Conditioner will work off and on and when they are not working you can get no air to come through any vent. There does not seem to be any ryhme or reason to when the air will blow and when it wont it will go on or off randomly doesnt matter if you just started the car or have been driving it for awhile.

Asked by for the 2000 Mercedes-Benz S430
I am having the same exact issue with mine right now....:-(