Heater blows cold air. on 1997 Ford F-150

When I turn the heater on regardless of how long I let the Truck warm-up it still blows cold air. How big of a repair job would this be?

Asked by for the 1997 Ford F-150
is engine coming up to temp on the gauge if it is not a thermostat in the engine needs replacement under 50$ if it is warming up the blend door motor has most likely falied 150-200$ ?? it is under the dash on top heater box
1 more answer
The repair will depend on whats wrong with the heating system. This no heat issue could be caused by low coolant level (may be a leak involved if so) and/or a plugged/clogged heater core.
Have you truck checked- the sooner you do the sooner you'll have heat!