I have a 2005 Chevy 1500HD 4X4 6.0 and the fan does not blow for the A/C or the heater unless your driving ( still no fan but blows while driving,hot air on heater and cold on A/C) would this problem be the blower motor or the blower motor resister ? Any help appreciated, just don't want to buy the wrong part ( I hate having to take things back).
Also does anyone out there have any good tips on getting better gas mileage in this beast ( besides just parking it, lol) ? I only get 9-10 mph.

 

unplug the motor and check with a voltage meter if you have power through all speeds if so probably the blower motor if no voltage at all could be the resistor or fuse