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Re: air won't switch to defrost vents
This system works with vacuum control doors. If you have a vacuum hose off under your hood it will cause this problem. Look on the passenger side near the evaporator - there should be a little round plastic bulb looking device - make sure it has vacuum to it. Also, check for other vacuum leaks in that area.
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Pull the control panel out of the dash and see if the mode control vacuum switch has a good vacuum source or the switch itself leaks vacuum. The mode control is what moves the doors that diverts the air flow around to the vents, defrost and floor.
I just fixed mine. The lever that opens and closes a door that directs the air flow to the defroster was broken. To be more specific, the plastic lever the actuator attaches to was broken. The actuator and the vacuum system were operating properly. It is simple to see but hard to get to. Remove the glove box and look up and to the left for a silver vacuum controlled actuator. I was able to fabricate another lever and attach it to what was left of the OEM lever.
Most common cause is a bad blend door actuator. This controls how the air is diverted, Sometimes the actuator will become stuck in one position. There are 2 types, a cable driven or electronic driven. Search for blockages underneath the dash that could prevent the actuator from moving. Also, it's possible (if it's cable driven) that the cable is either broken or loose to the point where it won't move the door any longer.
does it blow through the defrost vent only when you switch to vent/floor or does it blow through defrost and vent/floor? is it a switch that is just electric or a manual lever that you slide? the manual type will have that problem if the diverter or the linkage behind the lever(in the dash behind the panel......may be able to access underneath) becomes broken or disconnected so that the air is diverted to defrost regardless where you move it.if you can get to it, you will see what is broken or maybe a fastenerr fell off.
Have you checked the diverter doors under the dash??
It sounds like a vaccum hose may have fallen off your vent controller.
I have had similar problems and found that the air WAS moving, but it was all going up through the defrost vents at the windshield.
A quick check of the vac. lines showed that one under the glove box was pulled off.
with the engine running, try setting the air settings to all the options ( vent/floor/defrost..etc..)
See it you can feel or hear the diverters moving under the dash..