I have a GM furnace model# GBC-130LD. The blower will not shut off after the thermostat has clicked off and evacuated the plenum chamber. The blower runs 24 hrs. a day. I have tried to adjust the fan on temp. adjusting screw but nothing happens. How can I cycle normally?

1st thing is to make sure the tstat is not set on fan/fan only,, it should be on auto

This has happened many times