Dont know what the problem is but i can tell you its a vacuum leak . the vents are vacuum operated and require air pressure to change between the vents and floor. the defroster is default setting you may have a vacuum line that has come undone but all i know is its somewhere under the dash.
Check your servos.
You have a leaking heater core. You might smell antifreeze if you turn on the defroster.
it won't stay on if your blowing it the floor or using defroster.
I have exactly the same problem on my 2000 Still looking for the answer
you have a vacuum leak check hoses, listen for leak on smaller hoses.vacuum controls the air that comes out of defroster , floor, or dash.
If it is coming from the tank: NO. If it coming from the bowl: YES!
Heat is coming from the engine.
under the floor directly under and behind pedals
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Most temp blend doors have an electric actuator. The defroster, dash vents and floor vents are usually run by vacuum.
You didn't mention what vehicle you have but in most vehicles the heater core is located under the dash on the passenger side. The heater core is known to spring a leak and show up on the passengers floor. Turn on the defroster and see if your nose senses the sweet smell of radiator coolant. The inside of the windshield my fog up when the defroster is turned on, this would also indicate a leaky heater core.
Try it with your lights on, its probably your Hi-lo dimmer.
He used a navy ship to sound the sea floor. He found out magma was coming out of the mantle and into the sea floor.
What causes heat to only come out of the defrost and vent but not the floor of a 1995 S10 Blazer?
Leaking heater core
Under the vehicle, bolted to the floor about half way up the passenger side.
the middle vents only supply air from the ac unit using a separate in dash fan. the floor and defrost vents come only from the heater
Finding coolant on the passengers side floor. Turning on the defroster and the inside of the windshield fogs up. Sweet smell of coolant inside vehicle.
For what purpose they are using drv valve we have building consist of 15 floor ; the hot water in some floor coming with high flow while in other coming very low; please advise
it is normal. when you use the defroster, the air conditioner is also working to help dry the air passing over the windshield. this moisture is condensed by the cool evaporator and drained through the floor of the car.
Water can get in when the firewall flashing is missing outside under the windshield cowling. The water gets into the heater/defroster system and then drains on to the floor.
My guess is you have a vacuum line problem under the hood. When the vacuum supply is cut off the system reverts to it's default position which is floor and defroster. Check under the hood for a vacuum line that is disconnected, pinched, collapsed, cracked etc. A common place for a vacuum line to disconnect would be at the vacuum reservoir. This is the black plastic ball that is attached to the under side of the hood above the brake master cylinder.
The Beetles have the two levers on the center console on either side of the emergency brake handle. One is the Heat on/off lever and the other is the floor/defroster lever. Push the heat lever all the way down to the floor to turn it off.
There is obviously a leak in either the firewall/cowl area or the window seal.