Air always blows from defroster vent
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Joined: Oct 2005
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From: Jacksonville NC
Air always blows from defroster vent
'95 Coupe. Manual AC system. AC and heat both work but no matter which button I have selected, the air comes out of the defrost vent, with a bit also coming out of the lower vents below the dashboard. Nothing from the vents in the dashboard itself. Everything worked fine last summer. Over the winter, I've used the defrost pretty much exclusively. By the time the windshield was defrosted, the interior was warm and I just turned off the heater or turned it way down. The other day, we had a warm day and I put the AC on and noticed the air flow problem for the first time. Not sure when the problem first occurred. There should be some sort of diverter door system that determines what route the air takes but my Haynes manual doesn't give any info on it and I don't have the FSM. Any ideas or pointers on how to go about troubleshooting this?
Safety Car
Joined: Jan 2008
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From: Vero Beach Florida
Instructor
Joined: Oct 2007
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Before you replace the vacuum controller, Check the three way check on passenger side of the plennum. Check to see if your Cruise control works. If it doesn't, Your problem is most likely the three way vacuum check valve located on the passenger side of the plennum. Since the vacuum from this check goes to both the cruise control servo and the other line to the vacuum controller, usually they both stop working together. If your cruise control does work, The problem is most likely the Vacuum controller connector, not the controller itself. The rubber nipples on the connector close off after many years and the vacuum to switch from defrosters to vents, ect. cant get thru to operate the system properly. If it is the controller connector, There are other posts to help. It's a doeable job but, it will take several hours to complete.
Pro
Joined: Jan 2009
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From: Austin Texas
'95 Coupe. Manual AC system. AC and heat both work but no matter which button I have selected, the air comes out of the defrost vent, with a bit also coming out of the lower vents below the dashboard. Nothing from the vents in the dashboard itself. Everything worked fine last summer. Over the winter, I've used the defrost pretty much exclusively. By the time the windshield was defrosted, the interior was warm and I just turned off the heater or turned it way down. The other day, we had a warm day and I put the AC on and noticed the air flow problem for the first time. Not sure when the problem first occurred. There should be some sort of diverter door system that determines what route the air takes but my Haynes manual doesn't give any info on it and I don't have the FSM. Any ideas or pointers on how to go about troubleshooting this?
Don't know if this will help, but it might be worth reading.
(From near the bottom at http://shbox.com/1/4th_gen_tech2.html#adjust_valves)
"Restore Airflow to the Dashboard Vents
This is a common fix for when the air no longer blows out the vents. When there is not enough vacuum to operate the actuators, they will only direct air to the floor and defrost ducts by default. Diagram of HVAC system.
An easy way to tell what part of the system may have trouble is to go to the vacuum check valve and test the lines back to the mode selector, intake manifold and to the vacuum tank. The check valve often cracks and is the source of a leak, so be sure to inspect and/or test it.
A hand held vacuum pump (like a Mityvac), makes testing pretty easy (your lungs can be used as an alternate vacuum source ;-) ). At the check valve, remove the hoses one at a time and apply vacuum to each and see if it holds. The line to the intake manifold will have to be removed at the manifold and plugged back toward the check valve for you to test the line for leaks. If you find a leak on a particular hose, you will have to trace out the cause on that section."
Instructor
Joined: Oct 2007
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The three way vacuum check is located under the passenger side fuel rail cover. Just pop the cover off. the check is near the back of the plennum. You'll see a vacuum line coming off the plennum that splits into two lines off the check. You can get a replacement at Autozone, pepboys,kragenolso at your local Chevy dealer. This will fix your cruis control as well. Good luck
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Joined: Oct 2005
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From: Jacksonville NC
Fixed!
Holy cr@p! 
Pulled the fuel rail cover and this is what I found:
Thanks for all the responses and assistance. Replacing it fixed the vent issue but cruise control still isn't working. Is there an indicator light on the instrument panel or anything which indicates that CC is on? I get nothing when with the switch in either position. (The labeling on the switch is too worn to read. I'm assuming that far left, towards the end of the lever, is off and center position is on.)
Pulled the fuel rail cover and this is what I found:Thanks for all the responses and assistance. Replacing it fixed the vent issue but cruise control still isn't working. Is there an indicator light on the instrument panel or anything which indicates that CC is on? I get nothing when with the switch in either position. (The labeling on the switch is too worn to read. I'm assuming that far left, towards the end of the lever, is off and center position is on.)
