1992 Heater Problem

[valastro]

Here is a problem I am having with my 1992 Town Car.
When switch is in auto mode the following items will work with no problem (def, def/htr, vent, max/ac and ac....

When I move the selector lever to heater only it does not work and also will not work when I flip the switch from auto to the manual low, med, high area.

Does anyone know where the problem may be? I had a problem years ago where I had to replace the control switch on one of the heater hoses. I do not think this is the problem as everything works except when I have the control in heater mode. Any help is appreciated. Thank you.