does this olds(guess'n cutlass) have a/c..
recheck that all the doors in the heaterbox are working..
I don't remember a shut off valve for the heatercore(like posted above) on g body's
it may bypass the heatercore when on vent and a/c that door might be stuck on vent, blocking all heat..
start car and get warm.. then touch upper and lower hear hoses, both warm...??
remember lt1 is reverse cooled.. do you have the heatercore lines reversed?? the water try'n to pump uphill through the core could stall the flow...