First post. 04 silverado 2500HD w/climate control. Its been a cold winter. Of course this happened just out of warranty. The heater motor stays on all the time, with ignition off . I am able to adjust the temp, but not the speed. the only way to turn on or shut off the blower is to pull the fuse under the hood. Any insight on this would be appreciated.

so i take it that when the ignition is on, the fan is designed to run all the time? if so, there must be a solenoid or some type of device that cuts the power to the fan when the ignition is turned off, and it is malfunctioning.

other than that, if it has a fan speed swich with an "off" option, there could be a short which would explain why the fan speed cannot be adjusted, basically the short is bypassing the fan speed selector switch in your dash and the fan is running as fast as the current of the short wants it to run... and i reckon that the fuse doesnt blow because the short isn't supplying enough current to blow the fuse? that's my two cents... i will hopefully know a lot more in a couple years when im in the IBEW apprenticeship and electricity will be my carreer lol so if you still have the problem then, i can help a little better than now :-)

Check for a stuck relay or the fan control module.
Also check the body/heater computer for codes.
MT

thanks for the info guys. Yea, I really dont get it. It acts like a short, but doesnt pop the fuse. Yes, there is a separate off switch. Does this even have a resister card with the digital fan speed control? I will start on this this weekend

thanks for the info guys. Yea, I really dont get it. It acts like a short, but doesnt pop the fuse. Yes, there is a separate off switch. Does this even have a resister card with the digital fan speed control? I will start on this this weekend

The fan and fan speed is controled by the HVAC control module.
You really need a HVAC/body capable scanner to do any testing on it.
The fan speed is controlled by a digital signal from the module.
You will need a lab scope to read a digital signal.
I would check and look for codes past and present.
Also will the fan stop if you pull HAVC fuse 1.
The fuse should have no power with key off.
If the fuse has no power key off and fan keeps running the problem may be a HAVC control module.
If any codes post back codes.

For more info on testing and how the system works and a wiring diagram and repair flow charts.
I would suggest a all data online sub.
http://www.alldata.com/products/diy/index.html

Good Luck and
Let us know how it goes.
MT

i second the above.. ive seen a small handful of failed hvac modules between 99 and 05 trucks come in the shop.
chris