i have not air blowing out of my vents no matter what position it is in.
what are the common causes for this problem?

 

What year? Older trucks used to have a cOil type thingfor controlling the blower motor, if t let go you would lose fan speed selection

 

Does your fan work?

 

If the fan doesn't work check under the passenger side dash, there is a plug that I'm willing to bet is burnt out. I had the same problem

 

its a 1997 what plug are you talking about? No the fan does not work at all nothing will come out of the vents.

 

Where the plastic plugs connects to the blower it is common for it to melt. You can get a new pig tail on ebay cheap or at a junk yard. While your at it replace the rheostat. The new ones are a different design less prone to failure and put off less heat. The rheostat on my truck was inside the blower enclosure the fan keeps it cool as it produces alot of heat. Its about the size of a deck of cards.