Hi, I have a '03 Chevy 2500HD 4x4 6.0. I am having a problem with the blower motor speeds. When I start at speed 1 and go through 2, 3, 4, and 5 they all work correctly. When I go from 5, 4, 3, 2, 1 it is stuck on 5. When I turn the control off the blower goes off then I can start working my way back up until I get to the speed I want. This has been happening for a while and recently only some of the speeds worked. That told me the resistor went out and I had to replace it. So I did tonight. Now I still have the same condition of being able to turn it up but not down. I have a feeling the reason the resistor went out was because I was constantly turning the blower off and back on to get the speed I want. Is this a Climate Control Module (located in the face of the dash) or a Blower Motor Relay (located on the evaporator housing) or something in between? Any suggestions?

I did a little research today and a couple things may be incorrect about my last post. First, the only place I could find a relay was Autozone and it said it was on the evaporator housing. After looking at a schematic, I found that the blower motor relay was part of the resistor assembly. I have replaced that and still have issues. The other thing is that when I started turning it from 1 to 2,3,4 there was a noticable change in airflow. When I went from 4 to 5 I could not feel a difference. Whether there was or not would require checking the voltage to see if there was an increase. I may end up doing that even if it doesn't really tell me what the problem is. So it is down to the control module and wire harness. Because this is a manual contol module I can't imagine there is a problem with the switch. The way it acts it sounds like some kind of logic control gone crazy. Any ideas would be much appreciated!

I think you may be going down the wrong path. The A/C control in the dash is electronic and can go bad. Unfortunately, that part is a dealer item, so if it is determined that part is bad, you don't have a choice.

The other possibility is the Body control module....this also makes decisions related to the climate control.
The BCM is available, but requires programming after installed. This can be done at a dealer or qualified repair shop that has the correct tools.

2003 Chevrolet Silverado 2500 Hd Body Control Module - AC Delco, Cardone - TheAutoPartsShop - TheAutoPartsShop

This may be a situation where a professional diagnosis is needed.