Ok fairly pleasant NJ morning today I'm about 30 minutes into my 45 minute commute have the fan on with temp setting all the way down with the direction set to dash vents to bring in some cool fresh air when suddenly HOT air start coming from the the vents as if the temp controls have been pushed up to the very top!? No adjustments or turning off of fan, switching to air conditioning change the the temp from being HOT. Check gauges not overheating or anything else out of the norm. Get to work shut off truck, wait a few minutes and restart and now I'm back to getting cool air out of the vents. Never had anything like this happen before so would appreciate any suggestions of where to start to look. 2005 1500 W/T V6-5speed Silverado. In the meantime I'll try to keep my cool! Thanx in advance for any & all help.