ECC With a mind of it's own

aviator · May 4, 2005

I've recently traded in a much-loved '02 Avalanche for a used '04 2500 4X4 Crew Cab 6.0 with 27K miles. One of the options it has is the Electronic Climate Control, which is a great idea, but mine seems to have a mind of it's own.

I can start the truck, put the ECC in auto mode, set the temp and drive off. For Example, I can set it to 75 Degrees and the dash vents flow warm air, it's 48 degrees outside. a few minutes later, the ECC changes the vents being used from the dash vents to the the defroster The temp doesn't change.

Once the system has switched to defrost, I can't get it to change to any other vents, even by taking it out of auto mode and manually selecting other vents and changing the temperature (up or down) but the temp will change; it always blows out the defroster vents.

Now, once I turn the truck off, then back on, it will switch the vents to where they are supposed to be according to the read-out. Eventually it will go back to defrost though if I put it back in "auto" mode.

What's going on? Does it sound like I have a defective unit or is it supposed to use the defroster as it's main outlet for conditioned air? Sorry for the long post, but I tried to be as detailed as I could.

Any help would be appreciated.

71GMC_3/4T · May 4, 2005

Mine never goes to the defrost vents on Auto. There is a defrost pushbutton on the control module I have to press to get it to go to defrost. Also, when it's in defrost mode, there is a defrost indicator on the screen of the module (looks like a windshield with squiggly lines on it).

Maybe your pushbutton for defrost is sticking on. If you cycle between defrost and auto does the indicator change on/off?

aviator · May 4, 2005

Yes, the indicator changes from on to off and back when I cycle through. I thought the same thing initially, until I saw that the indicator was working properly.