Your blend door could be out of alignment, causing a mixture of cold and hot air to come out of the vents. If you cannot get just hot air or just cold air out of the vents, look into this further by checking the blend door out underneath the dash. Also, there is a valve on the firewall inside the engine that allows hot water to circulate through a heater core. This valve my be broken or stuck, causing the hot/cold issue when the air is blowing out of the vents.
Tuesday, March 19th, 2013 AT 9:26 PM