No Heat At All

my77' sedan deville does not blow any heat.i've had my thermastat,and heater core both checked.there both fine.it just blows cold air.please someone look out for me and help a caddy lover?? :banghead:

did you replace the heater core or just looked at it. with mine, it turned out the it was bad.
another possibility is a vacuum controlled switch that controls the amount of hot water to the heater core.