My borther-in-law has a 2003 3/4 ton Silverado and he's telling me the heater blower motor only works on high, no other speeds. Anyone have any ideas?

 

I had same thing on a '95. I had to replace the entire heater/ac control unit since you can't replace just the fan switch individually. Not cheap.

ChevyBlues

 

save your $ 02Lightning, and check the relay & hi-low speed controller on the heater box. when it only blows on 'high' it usually means the speed controller is gone. this is the one that goes into the heater box assm. @ the top, and has 3 different sized coils on the back side of it. i'm not saying the heater/AC control is not the problem, but this is going to be alot cheaper to replace. i used to have the values for the resistance of each coil to check if it was bad, but i can't seem to find it. before u replace the speed controller though, try tapping on the relay, which is usually mounted 2 the side/front of the heater box. if this doesn't change the speeds @ which it will operate, then go onto the speed controller. see how this works out 4 u.[sm=signs003.gif]

 

check your blower motor resistor it happend in my 1995 chevy 2500 what happens is the fuse blows but there is a bypass on the resistor to allow for you to still have heat. It will be located near your blower motor look in a chilton manual or just look online to see what it looks like though it probably faces down inside a compartment so I cant really explain what to look for. Its a $10 fix not bad at all