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1997 LeSabre redirects airflow to windshield under acceleration...

LBZNick

Buick Newbie
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I have a 1997 LeSabre with the auto climate control. Under acceleration, the AC will start blowing on the windshield, then back to the vents as normal as soon as I'm done accelerating. From what I've read so far, this seems like a vacuum issue. I'm wondering if it's just a leak somewhere I'll have to trace down, or if these cars have a check valve that goes bad that can cause this.

I believe the blend door actuator may be bad as well, because the HVAC system blows heat through the passenger side vents no matter what the system is set on. If it's set as low temp as possible on AC, cold AC will blow from the drivers' side vents while hot air blows from the passenger side vents. I'm wondering if the actuator being bad could affect the issue with the airflow being directed to the windshield under acceleration as well. Thanks in advance for any insight!
 
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BuickGirlFromMars

Well-known member
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1,193
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Buick Ownership
1999 Buick Park Avenue Ultra (Supercharged) , 1977 Buick Electra Limited (350 SBB)
I have a 1997 LeSabre with the auto climate control. Under acceleration, the AC will start blowing on the windshield, then back to the vents as normal as soon as I'm done accelerating. From what I've read so far, this seems like a vacuum issue. I'm wondering if it's just a leak somewhere I'll have to trace down, or if these cars have a check valve that goes bad that can cause this.

I believe the blend door actuator may be bad as well, because the HVAC system blows heat through the passenger side vents no matter what the system is set on. If it's set as low temp as possible on AC, cold AC will blow from the drivers' side vents while hot air blows from the passenger side vents. I'm wondering if the actuator being bad could affect the issue with the airflow being directed to the windshield under acceleration as well. Thanks in advance for any insight!
check valve, there is a check valve in your lines somewhere missing or bad. The check valve is what keeps your hvac from changing when manifold goes from vacuum to nothing
 

2007LucerneCXL

Full Member
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Buick Ownership
2007 Lucerne CXL. and 1995 Lesabre currently, past 1973 Riviera, 1968 Riviera
Here are diagrams on the two systems and various vacuum connections.
9706194H09-015.png 9706194H09-016.png
______________________________
 

imidazol97

Top Dog
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Poster doesn't say how long of harder, open throttle, acceleration it takes before the
vacuum drops and inside vacuum diaphragms revert to safety position and air goes
to defrost.

I'd suggest poster inspect the rubber around the one-way valve very carefully. IIRC,
there is rubber tubing in that area. The other is a nylon like plastic.

You can take the one-way valve out and apply suction with your mouth to see how it
allows air to flow and not to flow. That will tell you if the VALVE is working as designed.

I'd also inspect the reserve bottle under the front fender, in front of the wheel splash guard by looking
up. Loosen the connector there which likelyl is stuck after years in place. Then start the car
and with the inside in operating mode turn off the engine. Then remove the connector
at the bottle to see how quickly the vacuum drops. Inspect that bottle for cracks and any other
problems with the connector. If you can run the engine, turn it off for 1 minute, then remove the
connector there and be rewarded with a good whoosh as air rushes into the bottle and the
system, things are working well. Maybe the engine is worn and requiring a wider throttle
opening lowering vacuum from the engine over a period of time letting the inside diaphragms
relax.

The last place to inspect is the diaphragms themselves under the dash. Each has a hole in
the back side where you can place your finger to see if that diaphragm is activated or
relaxed. While difficult to detect, you may have a diaphragm with a small tear in it from
age letting in air while the system is trying to evacuate air from that diaphragm and
activate it.

With the engine running, and by switching the settings, you should be able to feel each diaphragm
flex at some time in the cycles to pull the doors into the needed positions.
 

imidazol97

Top Dog
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The poster's second problem likely is the electrical actuator on top of the programmer box
since it sounds like he has a dual control system. The actuator can have the inside gear crack
and that lets the gear slip on the hub that it's trying to rotate.

Or the actuator is dead.

While inspecting the action of the 5 diaphragm vacuum motors, the poster needs to watch
the movement of the two metal rods one on the top and one on the bottom of the
HVAC box from the programmer box attached to the right of it. Move the temperature settings
with a car that's warmed up and with the AC on.

I believe, believe, the
lower one is the driver's temp blend door and the one on the top is the passenger side
blend door control.

Both should move after delays waiting on input from the computer when it's requesting
action based on the inputs to the computer box. IIRC both of the snap loose from their
rods (the bottom one looks like it has screw threads, but those are just ridges and
it snaps off the white bracket easily.

With each one snapped loose, you can move the rod to move the blend door. If there's
no change in temperature in the air coming from the HVAC, that blend door may have
come loose from the rod. The manual control test here is the ultimate to determine
what kind of problems you have.
 

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