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depending on what year and make it is, the most likely issue is that you have a valve that moves to divert air to the upper vents, floor vents, and defrost vents and it is either stuck in the defrost position, is broken, or a cable/connector has come loose. The valve is usually in the center of your dashboard up against the firewall.
The air flow direction in many vehicles is operated by vacuum controlled servos. If the vacuum supply is cut off, the system reverts to it's default position which is the defrost mode. My guess would be that the HVAC vacuum supply line under the hood is disconnected, pinched or collapsed.
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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.
AC vents blowing through Defrost and bottom vents 05 crown vic?
2003 crown vic air conditioning vent dont blow
What would cause smoke to blow through the defrost of a 1990 Ford F 150 while the heater is switched on?
In many cases leaves can cause smoke to blow through the defrost of a 1990 Ford F 150
Why does a 2003 Crown Vic with auto temp control blow heat and ac from the defrost and floor vents but no air through the dash vents?
Because the air selector died.
What would cause air to only blow from the defrost and floor vents and not blow out of the panel vents even when the switches are turned to the panel vents in a 2002 Ford Explorer?
Any of the following can cause this......... 1. Bad a/c - heater controller.. 2. Bad a/c - heater controller inside door operation.. 3. Bad, broken or cracked vacuum line/lines..
Why doesn't heat blow out floor only?
the heat blows out the defrost when it should blow out floor vents only
Why does your heater only blow through the defrost vent on your 1994 Ford F150?
Idk know but mine does it when i start off from a red light or stop sign and as soon as i let off the gas or it changes gears (automatic) it comes through the vents like normal.
Why does your F250 diesel 6.0 when idling blow cold air through the heater vents?
most likely it's a bad thermostat, or your vents not working properly.
Why would the air only blow out of the dash vents but not my floor or defrost vents in my 2005 Chevy cavalier?
Check the following.......... 1. Vacuum leak, broken vacuum line or disconnected vacuum line. 2. A/C - heater inside car door operation.. 3. A/C - heater controller..
What could the problem be on 1988 Ford Aerostar when AC blows air out dash vents and floor but heater and defrost do not blow any air at all?
A vacuum leak, or one of the doors is sticking/bad vacuum motor in the heater box.
Why AC won't blow out of dash vents just defrost vents in a 1996 buick regal?
on your car it is a defalt mode for air to blow out defrost when there is no vacumn from the engine so you should look for a broken vacum line or see if it has come unplugged on the engine.
Why does ac and heater on 2000 f350 blow air through defrost when another position is selected ac clutch clicks and air still only blows through defrost?
You have vacuum line leaks somewhere.
