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usually one of two things. 1 the switch control may not be working. 2 under the dash are dampers which control the air flow direction. check to see if the vacuum lines going to the diaphram on the dampers have a vacuum leak, you may hear a hissing sound and possibly the engine running a little rough also, but not necessarily both. most cars I have worked on with this problem have had just a vacuum leak on one of the lines. try tracing them down from one end to the other.
What else can I help you with?
Why does air blow through vents on the dash but not through the defrost vents on top when you switch the control?
When you switch the control to direct air through the dash vents, the HVAC system redirects airflow away from the defrost vents. The system uses a series of blend doors to control airflow direction, and if the defrost setting is not activated, those doors remain closed, preventing air from flowing through the defrost vents. Therefore, air is channeled exclusively to the dash vents instead.
Why does your trucks defrost vents start smoking?
That's probably steam from a leaky heater core.
Why does AC and heater blow air through defrost vents and will not blow air into cabin vents in your 2009 Mercury?
If the AC and heater in your 2009 Mercury are only blowing air through the defrost vents and not into the cabin vents, it may be due to a malfunctioning blend door actuator or a problem with the HVAC control system. The blend door actuator controls the flow of air to different vents, and if it’s stuck or malfunctioning, it may be directing all air to the defrost vents. Additionally, issues with the climate control module or vacuum leaks in the system could also cause this problem. A thorough inspection of the HVAC system is recommended to identify the exact cause.
Why heat blows out vents only not defrost or floor?
Most likely a bad or disconnected vacuum hose to the defrost/floor selector in the heater ducting.
Why does heater defrost vent not open on a 1989 Sunbird and cold air blow from dash vents but no air blows from heater defrost vents and where are the enter and exit hoses for the heater coil?
I don't know why the vent would not open for the defrost, but it may be related to the fact that your heater core is blown. If your getting nothing but cold air out of the vents when the heat is on, your core is finished and if the core is finished then it is likely related to your vent not opening/switching. Something''s wrong with your heating either way.
Why does AC and heater blow air through defrost vents and will not blow air into cabin vents on 2002 Oldsmobile bravada?
If the AC and heater in a 2002 Oldsmobile Bravada are only blowing air through the defrost vents and not into the cabin vents, it could be due to a malfunctioning mode door actuator. This actuator controls the airflow direction and may be stuck or broken, preventing proper airflow to the cabin. Additionally, a vacuum leak in the HVAC system can also affect the distribution of air. It's advisable to have the HVAC system inspected to determine the exact cause and resolve the issue.
Selector only stays on defrosted 92 buick?
If the heat selector will not switch from defrost to the dash or foot vents on a 1992 Buick, it is possible that the cable connected to the vent is broken. When the selector is moved from defrost, a cable opens the other selected vents on the heater.
Car heater just defrost work?
When you set the control, if you chose defrost, it usually does it at the temperature you specify. So if you want heat only blowing through the windshield vents, which I believe may be the question you are asking, it varies between makes of cars. This is what to look for : defrost, fan speed, temperature. If you mean "Can a car that only has a heater ( no air conditioning ) be used to defrost?" The answer is still yes. I believe the question is missing words. It is comparable to asking "Hand, just finger work?" You might try asking again, being more specific, explaining why it is a problem.
Why do you get hot air at floor and defroster vents but only cold air at the dash vents vents in a 1995 chevyvan 20?
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
What causes the front air conditioner on 1999 Lincoln navigator to stop blowing through the ac vents and start blowing through the defrost vents?
When there is a problem in the vent system it defaults to defrost setting. Check the doors & vac supply
How do you know which heater core you need to replace on a 94 ford aerostar front or rear you have heat but no defrost and stream comes out of the vents when heat is on?
Front heater core is in the dash, the rear heater core is all the way in the back of the vehicle. If you have steam coming out of the dash vents, the front HC is leaking. If you have steam coming out of the rear heater vents, then the rear core is leaking.
Does the heater vents on a 2004 2500 dodge diesel operate on vacuum or electric My truck only blows out of the vents on the dash occationaly it will switch to defrost for me?
The doors are electric. You most likely have a broken door inside the heater box under the dash.
