Hey y'all I have 98 5.4l. Within the last couple days I havnt had any warm air blowing through the vents. I'll have the truck running for an hour and still nothing. Could it be my coil or my thermostat or something else?

 

Wow; this problem is like an epidemic around here.

I assume the truck doesn't overheat and runs normally? If so, try backflushing your heater core (disconnect both firewall hoses and run garden hose water through the outlet until it runs clear). It takes all of 15 minutes and costs nothing except the price of a quart or two of coolant.

If that doesn't fix it, your HVAC blend door may be malfunctioning, but from what I've heard that's usually accompanied by a noise from the dash when you turn the center ****.

Do a forum search; many threads on this.