One problem related to defogger has been reported for the 2004 Chevrolet Avalanche. The most recently reported issues are listed below.
My heating and air conditioning system does not function correctly. It has a mind of its own. It adjusts itself from hot to cold, cold to hot. It adjusts itself from low to high, high to low. Occasionally when I shut of the truck and take the key out the heating/cooling system will remain on. I can't drive in cold weather particularly in the morning or when its raining afraid that my defroster/defogger wont work because of the problem.