Brake pedal firmness changes with air conditioning

[anawrot]

I just noticed today that if I have pressure on my brake pedal and I turn off my a/c, I can feel the pedal sink slightly (resistance decreases). It's totally repeatable. When I turn the a/c on, the brake firmness increases slightly.

I flushed the brake fluid a few weeks ago and it was clean without air bubbles.

Anyone ever notice this? Are the two systems connected at all?

[cstang68]

It is due to the idle rpm. When the AC is on the car has a higher idle and pulls more vaccum. So when you turn off the AC the idle falls slightly and the motor is pulling less vaccum, which leads to less "vaccum assistance".