When the fan/blower is switched to the off position, the floor vents open, blowing hot air while driving. Is this some kind of 'fresh air vent' that I just need to close? When the blower motor is on, all vent options (floor, panel, defrost, etc.) work properly. However when the blower is switched off, the floor vents open and heat the cabin quite effectively. Tired of sweating!
I the short answer is yes. The truck has a flow-thru vent feature as does most GM products. When the fan switch is off the outside air would flow into the truck.
I thought you could still direct the air by way of the control panel, but by the wiring diagram it looks like everything is disabled when the fan switch is in the off position.
Short answer to what is yes? Yes I'm stuck with hot air blowing through my vehicle? In that case I have a nice 99 suburban for sale with permanent heat.
Yes it has a fresh air vent that is open when the fan or the main control is in the off position. The air should not be much hotter than outside air, so if it is going thru the heater there is a problem with one of the blend doors.
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SOURCE: Heat wont blow through heater or defroster vents
The door in the heater box is most likely stuck. It is located under the dash on the passenger side
SOURCE: heater control 98 chevy s10 blazer
These trucks have a problem where moisture builds up in the heater box then freezes. When this freezes and you change your heater settings it breaks the shaft for the blend door. If this is what happened you should be able to look under the dash above and to the right of the gas pedal and you will see two vaccuum accuators one of them you should be able to wiggle around the linkage if it is broke. To fix this you need to remove the entire dash to get the heater box out which involves discharging the AC and draining the coolant because the heater core and evaporator come out. Please rate.
SOURCE: 1998 Mustang - AC blows only through Defrost vents
You probably have a vacuum leak on the passenger side. its a small plastic hose some times they come unpluged from the engine. or brake.
SOURCE: Heat wont blow through heater or defroster vents
common problem, check under dash by the gas pedal if control arms are muving went selecting from ac to heat cuz this it is the control for the vents to go from ac to heat and to defrost.
SOURCE: PROBLEM WHEN SELECTING THE DIRECTION FOR THE AIR
Sounds like you have a supply vacuum problem. When you lose supply vacuum to the control head it defaults to defrost.
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The heater box door seems to work just fine. The actuator seems to be fully functional when the blower is on. It switches from floor, to panel, to defrost, and everything in between just fine. However when the fan is switched off, the actuator opens the floor vent.
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