So recently purchased a 2005 Sierra crew 2wd. It has the auto temp climate control. Noticed that the a/c blower will not go down to the low speed. Stays on the medium to high setting even when you turn it down on low. If u turn it up it will go higher. Also noticed the blower is pulsing. Kinda like it is cutting power to it at a constant rhythm. Only stops this rhythm if u turn it up on high. I have replaced the resistor/module with the “new version” which required me to re wire it. Also replaced the blower motor itself with a new one. Today I went to the salvage yard and replaced the hvac control head and got the same results. Nothing I have tried has changed the issue.
Can you share the part numbers and brands of the replaced new parts?
Do you have scan tool to check HVAC codes and data?
Do you have a multimeter and experience using one?
Gonna borrow scan tool tomorrow. Can get and use multimeter also. The new parts were blower from autozone and the replacement resistor was a China knock off from eBay.
You will need to go back through your processes to try and remember if the problem you have now is exactly the same as before any parts were replaced or if they could be slightly different.
The “pulsing” symptom is interesting because it would indicate very coarse control. The system uses a pulse width modulated signal to make the blower work at various speeds.
I am including a link to a repair article I did a few years ago. The year is different but the parts are the same between the years. keep in mind that all testing was done with ACDelco replacement parts.