I have a 2000 5.2L 4X2 and everything has been working fine until the other day when I went to turn on the heater and nothing happened.... Fan doesn't work on 1, 2 or 3 but blows really well on 4. I get heat and cool on 4. I get some heat and cool air on the lower settings but only feel the air coming through the vents when I'm moving/accelerating at significantly less than what it should be on that setting. Any ideas?

 

sounds like your resistor's shot do a search on blower motor resistor

 

That was it. $50 bucks and less than five minutes. 2 screws under the passenger side dash revealed a very brittle ceramic blower motor resistor. Yay. I have settings again.

 

glad i could help..