Ac/heat issue


New member
Buick Ownership
99 lesaber limited
Hello, i have a 99 lesabre limited. The ac/heat will only blow thru the center vents. No floor or defrost. Also driver side will blow heat and ac, the passenger side will only blow ac. I replaced 1 vacuum line and when i did it started blowing out the floor and defrost at the same time and would not switch to vent. I am a little lost here. Any help would be greatly appreciated, thank you.

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Top Dog
Turn the engine off for several minutes. Turn the key to ON and see if the air is blowing out the defroster.
That should be the default with no vacuum. If your system does not go to defrost when the vacuum diaphragms are
relaxed, then you have to troubleshoot another way.

You need to make sure you've got full vacuum to the programmer box under the dash on the passenger side.
Take off the underdash plastic panel: it's only a couple of screws IIRC. Find the inlet vacuum line, black IIRC, that
connects to a violet one that goes to the programmer box. They are a press fit but it likely won't want to slip
off easily because it's been connected forever.

You hold your finger over the end of the incoming black line and should have really good vacuum there.
IIRC, the vacuum starts on a rubber piece at the intake manifold next to the big vacuum line for the brake booster.
Then there's a nylon line that runs over to the passenger side bundled with electric wires. That meets a line
with the one-way valve in it. That line has a T that lets a line go inside the car and the same vacuum goes
to the reservoir under the front fender. Look for bad rubber from age and hardening. Especially likely at the engine
connector due to heat.

The plastic reservoir may be cracked causing a leak. With the engine running, then turned off, pulling the line off at the
reservoir within a few seconds should give a great whoosh as air rushes in where you just disconnected the region
of stored vacuum.

If you don't find your problem there, then it's doesn to trouble shooting the interior lines and the vacuum diaphragms.
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