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Old 08-05-2010, 08:28 PM
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No Air coming out of defrost only front vents

Hey guys/girls.,
Im workin on a 95 pontiac grand am. The complaint the guys havin is when he turns the switch to defrost mode there is nothing happening only air coming out of the front vents. Now the fan is blowing nothing wrong there, i checked all vacum lines coming from the switch to all 3 vacum valves no problems there so i replaced the the vacum valves and still nothing. I am stumped. IS there a another vacum line im not noticing or what? Everywhere i checked said it could only be the lines or valves but when i disconect one of the lines and switch the switch i DO NOT feel vacumn coming from the valves them selves.... shouldnt i? anyways any help will be greatly appreciated! thnx

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Old 08-06-2010, 03:09 PM
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any help would be appreciated!
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Old 08-06-2010, 04:52 PM
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Okay , you said you checked the vacuum lines from the control to the servos , right ? I didn't see where you confirmed vacuum coming to the control . There should be a plastic vacuum reservoir somewhere (probably under the hood) . Let me know what you find. Confirm vacuum to the switch/control first and if not , trace back towards the engine from there .
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Old 08-06-2010, 05:19 PM
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Most vehicles default to defrost when there is no vacuum to move the servos, but that one could be an oddball, the previous advice is a good start,
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Old 08-06-2010, 06:10 PM
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Thanks for the reply,
No i am not getting vacum at the switch itself. when i put my hand over the connector that plugs into the switch there is nothing. I will take a look for that plastic reservoir later on tonite and see if i can find it. What am I looking for as far as malfunctions go? with that reservoir? Ive never done this kinda job before so im goin in blind but like i said i replaced what i could so far and got stuck haha.
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Old 08-06-2010, 06:30 PM
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Just get vacuum to that reservoir, and from there to the vacuum switch and you'll probably be good to go,
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Old 08-07-2010, 06:35 AM
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Quote:
Originally Posted by Rickracer
Just get vacuum to that reservoir, and from there to the vacuum switch and you'll probably be good to go,
The reservoir is a liitle bigger than a large grapefruit , round and black .
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Old 08-07-2010, 07:09 AM
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On my 94 Formula the hose goes straight from the controls to a tee in the vacuum line with check valves in it. Its located on the passenger side just in front of the firewall. But it has no reservoir that I know of.

Im with Rick, Im curious as to why its not defaulting to the defrost vents....
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Old 08-07-2010, 12:08 PM
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yes its definatley a head scratcher
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Old 08-08-2010, 12:30 PM
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The vacuum switch part of the controls is probably NG. You need to get a vacuum diagram.
Is the defrost mode the only one that doest work. Does it blow at teh floor when you put it on heat.
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Old 08-08-2010, 02:24 PM
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thats the thing tho, i replaced that switch cluster along with the vacum valves so that should be all good.... and no it is not blowing underneath just out of front vents hot/cold it is getting absolute zero vacum...... and now that i think of it i dont know if this would help any but when i put my hand over the defrost vent it almost feels like its SUCKING my hand down instead of blowing out???
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Old 08-08-2010, 02:33 PM
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In that case, Id trace the black vacuum feed hose that goes to the switch through the firewall into the engine bay and find out where its cracked or disconnected. Im still curious as to why itd default to the panel vents instead of the defrost vents though...

To make sure thats the problem you could simply pull a vacuum on the back of the switch and then see if the switch will make it blow outta the top or bottom vents.
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Old 08-08-2010, 02:34 PM
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Im gunna upload some pics here and see if u guys can get anything out of it more than i can.... instead of me trying to explain it haha be a bit easier!
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Old 08-08-2010, 03:07 PM
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If you think the defrost vents might be sucking just light a match and blow it out then hold it near the vents, the smoke will tell you what's going on. Or you could use a ciggy if your foolish enough to smoke
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Old 08-08-2010, 04:30 PM
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[IMG]p8089849[/IMG]
Ok this is the switch with the vacum lines connected to it

[IMG]p8089850[/IMG]
This is the vacum lines/ connector

[IMG]p8089852[/IMG]
This is the vacum valve on the passenger side which is connected to the trap door i beileve is for the defrost

[IMG]p8089853[/IMG]
This is another vacum valve in the center of dash and then there is another one right above it forgot to get pic of it

[IMG]p8089854[/IMG]
This is a line i have no idea for its just there it wasnt connected to anything... could be just a atmospheric vent of some sort???

[IMG]p8089855[/IMG]
This is where everythings connected underr hood i couldntt find no reservoir
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