1999 Pontiac Bonneville Air Flow

When the A/C is on in this car, the air flow is split between the defrost vents and the dash vents. I have read it may be a vacuum leak but don’t know specifically where to look for it. Is there any way to manually redirect the air flow? Any ideas on where to look for a vacuum leak? The air is cool but just misdirected.

Could be anywhere. If it uses vacuum pull motors for the blend doors…all of them and all the hoses are suspects.
Techs use a smoke test to find leaks. Youl just have to use your ears and follow all the lines . Up behind the dash will be a pain.

You could stuff socks in the defroster vents. Just not so far in that you can’t get them out. And use clean socks!

I’m seeing electric blend door actuators on this car. one of them is stuck , not working right or there’s debris in the plenum, Possible switch or wires.
But the blend door motors are most suspect as they’re a most common replacement part.

I love the sock idea… It’s hot here in Virginia! I sure would like to find those blend door actuator motors for a more permanent fix though. How do I find them?

Go to a GM dealer’s parts counter and ask them to show you where it is located. They have exploded views of all the areas of the car. You might ask how much they want for one while you are there. Check prices on line for AC Delco parts before you go so you can make an immediate comparison.

Do you have the automatic climate control or manual?

THe auto uses vacuum actuators to control air flow and temps. Usually one goes bad and you can figure it out by looking under the dash and watching as the move when control modes are changed. Or you could have a vacuum leak.

I appreciate the responses. As far as “automatic climate control” or “manual” I’m not sure. Here is what the Control Panel looks like:


Thanks for all responses and Happy Father’s Day to all the Dads out there!

That should be the manual unit. Just like the ETAC units it redirects vacuum to operate various doors which control airflow, etc.
Sorting this out may require a manual and a handheld vacuum tester.

A vacuum leak anywhere else in the engine compartment can have an effect on climate control operation so the first thing I would want to do is run a vacuum test which can easily be done with a handeheld vacuum tester or a vacuum gauge.

Another potential cause of problems is a one-way valve which is usually located under the hood and near the firewall. This thumbsized widget is designed to hold vacuum steady in the climate control unit rather than allow it to fluctuate due to various throttle positions.

Sorry I can’t be precise on this. It’s more than likely a vacuum issue and it will have to be tracked down one way or the other. There was a time when all of this was done with cables… :frowning:

I remember those cables… I never had one break either. Anyway, thanks for writing all that, I appreciate it. I will start the hunt for a vacuum leak and go from there.

That system is manual. The automatic system allows you to set a temperature and it controls heat and AC to match your desired temperature.