Question about 2006 Chevrolet Silverado
You are dealing with a vacuum leak. Vacuum operates the flaps that direct air through the heater core. When you are traveling at higher speeds there is enough excess vacuum to partially operate the system. Under the dash or under the hood , there is a vacuum line that is misrouted , kinked , cracked or unhooked . You will need to do a careful , methodical search of the vacuum lines to find the bad spot. I would start under the hood it is easier to knock or break a vacuum line there and not notice what has happened (changing spark plugs,changing oil , cap rotor wires, etc.). The problem could be under the dash , a pencil fell down a vent and is jamming the heater vent closed, again a cracked or unhooked vacuum line, or even a simple heater shutoff valve that is just not opening the way it should to allow the warm anti freeze to flow to the heater core. Depending on how loud the exhaust system is it may be possible to carefully listen for the leak with a tube to your ear . A tube will allow you to listen in areas that may be hard to access (under the dash). Good hunting.
Posted on Nov 14, 2010
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Posted on Jan 02, 2017
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