Heil DC 90 furnace- when heat is engaged only blows cold air through the vents
Any help would be apprciated. When the furnace is in hear mode...it ignites as I can see the flame through the little window in the compartment. The fan blows and the system kicks in. However, the furnace pushes out cold air through the vents. I changed the filter however this does not help.
How long does that flame remain on when the furnace is calling for heat?
Do you have a flashing diagnostic light that is visable through a viewing port or a grilled furnace door? There will be a legend inside the furnace (probably on the door)that will explain what that diagnostic flashing light means.