I have a 2004 Duramax with a heater switch problem. I hope someone has solved this problem before and can help me. The problem is the switch only turn on the blower at top speed #5 on switch. Anything else delivers no air, but when it does come on at 5 you do get the maximum delivery

Thanks for looking...........................Dan

 

One of two things:
#1 - the switch itself
#2 - the voltage divider circuit ( resistors ) I'm not sure if your 04 still uses the resistors or a more complex cicuit.

Hope this helps.

 

I had the same problem with my 1500. The fan speed selector would not work on the number #1 speed. Speeds 2 thru 5 worked fine. I took it to a local shop and they replaced a resistor. They charged $120.00. That's been about 2 months ago. It's still working.

Hope this helps,