I have a 97 B2500 with the 5.2 motor.
the hvac controls in the dash were all broken when I got it. However, I did get the blower to work on all settings. Since the switches were missing, I removed the whole unit and replaced with a new one(well, new to me from a donor van). Now I cant get anything to work, its like Im not getting any power to the unit(even the light doesnt work). so I figured Ive blown the fuse..nope. all good.
so checked the fuse in the power distribution center under the hood. they all look good also.
so...is there a relay or something i may have blown that supplies power to the unit?

 

so I got the blower motor to work, but it only works on high. so resistor needs replaced.
my problem now is that its only defrost that works, regrdless of what I switch to, everything comes through defrost vents. Im assuming a vacuum leak, but cant find it, any help?