Air Conditioning/Heater issue

[Doug Meloan]

Hey guys, need some professional/expert advice.  This morning when I started my 1963 Cadillac and turned the heat on, all it would do is blow out cool air from the lower (floor) vent. If I switched it to air conditioning, the compressor would kick on, but it would still only blow out cool air (not air conditioned) from the lower vent.  In other words both the heater and air conditioner settings do not seem to be functional.  If I slide the lower temperature control adjustment from cool to hot or from hot to cool, it makes no difference in the temperature of the air coming out.  Is this a vacuum issue of some kind and if so where would the likely culprit be?  Is there something else I could check as well?  It worked fine last time I drove the car. Thanks, Doug