Vacuum modulated AC?

[David1966]

I've noticed on my '94 LeSabre that when I have the throttle plate at a low vacuum position--accelerating onto a highway, for example--it seems to change where air is coming out of the heating/AC system.

Is this a design peculiarity of this model, or is there something wrong with the vacuum control system?

Thanks,
David

[tman]

If you step on the gas, tha AC will slow down to give more power to the engine, if thats what your asking.

Or are you saying instead of coming out of the upper vents, it comes out of the lower vents? Thats a problem with the flapper in the blower assembly.

[David1966]

Thanks for your help!

To be more specific, when I step hard on the gas, the air comes out of the lower vents rather than the upper vents, then returns to the upper vents as I return the pedal to a cruising position. If that is a problem with the flapper valve, is it vacuum related? Unfortunately, I don't have a full service manual for this car.

How does the car modulate the AC in response to demands for power? Does it disengage the compressor?

Daivd

[tman]

I'm not sure of much beyond what I told you, but I believe the compressor slows down, as if you had it on 60 and changed the temparature to 74.

[David1966]

I solved the problem of vacuum modulated A/C settings. I decided to replace all the vacuum lines, and in the process, I discovered that the plastic vacuum check valve on top of the engine had a crack in it.

Replacing the check valve solved the problem.

David