I have a 2000, 1500 Silverado LE. I was driving to Des Moines from Milwaukee Thursday and as I was driving I noticed that the cab was unusually cool. Of course this happened when the weather hit 12 degrees. Anyways I have checked every fuse related to HVAC. The coolant is at a normal level. I was however able to get a little heat by switching everything to the max position and then by selecting recirculating the air in the cab instead of from venting outdoors. If anyone has any ideas on how to go about finding out what else could be causing it, it would be greatly appreciated.