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Mainly because you don't need a fogged up windshield if you are driving fast. Seriously, the defroster setting is where most autos go to if there is a problem with vacuum. If nothing worked in your dash controls, the one thing you would still need would be the defroster, so that is the default setting. Now, when you accelerate fast, the throttle is wide open, and there is no vacuum, or it is very low, so with low vacuum the control reverts back to defrost. It would be the same as if you un hooked a vacuum line and did not feed your dash controls, you would only have defrost.
What else can I help you with?
Why is your air conditioning fan switching from vent to defrost on acceleration?
You have a leak in the vacuum supply to the ac control.
AC vents blowing through Defrost and bottom vents 05 crown vic?
2003 crown vic air conditioning vent dont blow
How do you fix the air conditioning if it only blows through the defrost and floor and not the vent in a 89 Chevy S10?
Check under the hood for a broken or disconnected vacuum line.
Why do most air conditioning systems not need a defrost system?
Dont no
Where is the central air conditioning vent located in the living room?
The central air conditioning vent is typically located on the ceiling or high up on a wall in the living room.
How do i clean the airconditioning on a 1998 Daewoo lanos?
You can clean the air conditioning by vacuuming out the air conditioning vents. You can also clean the air conditioning condenser vent screen.
What is the purpose of the AC vent hose in a car's air conditioning system?
The purpose of the AC vent hose in a car's air conditioning system is to carry cold air from the air conditioning unit to the vents inside the car, allowing the cold air to be distributed throughout the interior of the vehicle.
2001 ford ranger air conditioning will only come out of the defrost Is the switch bad for the vent control can you make the vent open manuelly?
Check for a vacuum leak either under hood or under dash Check the operation of the vacuum controlled motors under dash Check the operation of the selector switch Defrost is the default position for this system
What causes the air to stop blowing out of dash vent when accelerating?
you have a vacuum leak
Why do most air conditioning system do not need a defrost system?
Because most air conditioning systems operate at a temperature above the freezing point of water.
Why do most air-conditioning system do not need a defrost system?
Because most air conditioning systems operate at a temperature above the freezing point of water.
When accelerating or engine under load of 2002 f-250 ac air from dash vents moves to defrosters then to floor while cruising it works fine any ideas?
you have a vaccumm leak defrost is the normal at rest vent setting
