1990 Park Avenue Heating Problem

I just bought a very nice 90 Park Avenue. The problem that I am having is that I noticed last night that I was not getting any heat from the blower when I turned it on even though I raised the thermostat all the way to 90 degrees. The control on the dash seems to be working correctly. Any ideas as to what may be causing this problem?

Do You Have A Gauge For Engine Temp On Dash? What Does It Read? I Think Its A Stuck Thermostat, Not Letting The Engine Get Hot Enough To Warm The Heater Core. Another Thought Is A Clogged Heater Core. Let Us Know What You Find. Please Do A Bit More Investigation It Will Help Us Determine Your Problem Easier. Thanks.

Mike.