'89 Audi 100 Heater questions

[Case and Mary]

All,

Now that I have great information on the transmission, let's tackle the
heater.  No warm air comes out regardless of what we do in the passenger
compartment.  I did look under the hood and the heater regulator seems to be
functioning.  I am unfamiliar with this aspect of the car and only possess a
Haynes manual, which is one step removed from useless.  The temperature
readings seem to be correct as displayed on the dash and the air conditioner
works very well (we live in New Orleans, the heater is a nice to have, the
A/C is critical).

As always, thanks for the help!

Case