What's wrong with my AC?

The car is an 88 300E. The other day the ac stopped working all of a sudden. The ac won't work and neither will the heat or defrost. If you turn it on you can hear a low hiss for a second but nothing will blow. If I'm driving down the road the ac (and heater and defrost) will turn on and work but only at a very low setting regardless of where the button is (lo/hi/auto). What's wrong?
Thanks in advance.

[stevebfl]

Sounds like a bad blower motor to me. Maybe a blower controller but they don't fail that often on 124 chassis.

As always, thanks a lot stevebfl.

I just discovered that the blower motor was replaced in 8/99 about 12K miles ago. Is it possible that it failed again so soon?