my heater on my truck is only blowing cold air

Either the engine is not getting to operating temperature, which means the thermostat needs to be changed out, or it is low on coolant, or the cooling system needs to be purged from air pockets, or the climate control blend door is not working. Check to see if the heater hoses are getting hot.

Move the knob from cold to hot and back and listen for the blend door moving. If it is not moving it's either the door or the actuator motor. The motors are plastic and tend to break because they have plastic gears. They cost about 50 bucks each. Hopefully the entire dash does not have to come out to replace it.

Where is the acutuator locacated