I have a 91 Buick Riviera. The a/c when turned on does not blow cold, but when checked it is cold under the hood and has freon. Basically it just acts like the blower motor comes on. In the winter there is no hea, but again the blower fan comes on when the car calls for heat (it has a digital dash that you can set the interior climate control up to 90 degrees) but it still blows cold when the thermostat turns on the heat. The heater core was replaced last winter and it all worked fine, bot the heat and Air. I can't figure out what can be causing this. Please help.