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Dave Nova
Dave Nova, Pontiac Technician
Category: Pontiac
Satisfied Customers: 19452
Experience:  ASE Master Certification. GM World Class Certification
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Pontiac Grand Prix GTP A/C air blows from vents and floor

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A/C air blows from vents and floor only. Changing mode switch does not change to floor only or vent only. 97 Grand Prix GTP with dual climate control

Hello and thank you for using JustAnswer. My name is XXXXX XXXXX I will do my best to help you with your Pontiac problem.


Your car should have a set of vacuum solenoids (#2 in picture below) under the passenger side of the dash that control the modes (vent, floor, defrost). Start by checking for vacuum at the source hose (#3 in the picture below). If you have vacuum at this hose with the engine runniing, then check to see if the solenoids click as you change modes on the control panel. If the solenoids click, you will need to check vacuum output from the solenoids to the vacuum actuators that move the doors.


Picture from under passenger side of dash looking up. Arrow points toward front of car.





Customer: replied 6 years ago.
Looks like no vacuum at the source hose. Do you have some pictures to help me find the other end of it under the hood?. I found one plastic vacuum line running along the right fender(looking forward) under the hood that was broken. I repaired the break but that line goes forward under the windshield washer fluid tank so I don't know what it goes to...but fixing it did not bring any vacuum to the source line for the mode solenoids.

In the diagram below, #3 should be the connection at the engine for the a/c vacuum hose. This is near the throttle body.




This vacuum line will tee off and one side runs inside the car. The other side should go to the front of the car on the drivers side to the vacuum reservoir. This is mounted below the fender.



Customer: replied 6 years ago.
The one that runs forward (to the vacuum reservoir I presume) actually is the one I fixed and it runs on the passenger side (not driver side). What would the break in that live have been affecting?
I still can't find a line that runs from there thru the firewall. :-(

If the line that runs to the reservoir is broken then it could reduce the amount of vacuum available for the inside controls. Look down low on the passenger side of the firewall for the wiring harness. The vacuum line comes through the firewall with the wiring harness. This will give you a location where you can hopefully find the vacuum line and trace it until you find the break.

Customer: replied 6 years ago.
Hi Dave...could not trace that source line thru the firewall..too far down behind the engine..can't see or feel down there, so instead I went after the line that comes off #3 on the intake manifold and goes forward along the pass. side fender.
It goes under the washer fluid tank so I removed that..pulled back on the line and sure enough it pulled out a broken off piece of line that I'm guessing is supposed to attach to the vacuum reservoir. Wherever is goes is beneath the battery and I didn't feel like taking it out. However, what pulled out was a t-fitting. The side going down had the broke piece. The t-side had another line that runs back under the motor. On a hunch, I attached the line coming from the manifold directly to the line under the motor and lo and behold it must be the source line for the A/C solenoids...they now work fine.
Since your initial recommendation sent me in the right direction I'm ok with signing off on this, with my thanks.
I do have two more questions though that I'd appreciate a reply on:
1.) Apparently the vacuum reservoir has been disconnected for some time, and still is since I bypassed the broken t-fitting. What effect would that have on anything?
2. The t-fitting itself fell apart as I pulled back on it. It looks like it maybe has a one-way valve in it. Would that make sense? Do you think I could get a direct replacement from an auto parts store, or would I need to go thru a dealer? OR....could I just replace it with a straight t-fitting?

Your final follow up on this would be appreciated. I'll sign off on this after I hear back.
Thanks again for pointing me in the right direction.
To answer both of your additional questions at one time: The vacuum tee is a one way check valve, you can purchase vacuum check valves at any parts store, does not need to be the dealer. What happens under normal operation is that the engine produces vacuum, then goes through the check valve to the reservoir and to the inside of the car. This way when you go to wide open throttle, there is still vacuum reserve available and your vents continue to work as they should. You will at least want to use a check valve. If you do not reconnect the reservoir, you may lose vacuum to your vents under a period of long acceleration, such as passing on the highway or pulling a long hill. You do not need to pull the battery to get access to the reservoir, best way to get to it is to pull the plastic panel under the bumper/fender. Please let me know if you need any additional information.
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Customer: replied 6 years ago.
Excellent! Thanks again...and for the information on how to access the reservoir.
You are welcome. Thanks for using justanswer.