Losing Brakes with A/C on.

TheEmrys said:

I just had an odd little problem. With the A/C on, I lose a good portion of my brakes. It seems like I either have a problem with my A/C or my brakes. My first thought is my brake vacuum booster is having issues keeping up with the amount of vacuum needed when the A/C is running. Anyone else have any thoughts? I'm ready to hit the auto-parts store and replace it, but if anyone else has had any other ideas, I'd like to hear them.

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I would think there is a vacuum leak somewhere. Its not the booster since it works fine without the ac. Its it only at an idle? Does the idle boost come on?

It is reduced any time the A/C is on, around town or on the highway. I just drove LA to San Diego and it was this way all the time.

Try this: Start the car up, let it idle for a minute or two with the A/C off. Turn the engine off. Wait another minute or two. Press the brake pedal a few times. Was it easy to press at first and got firm after pressing it a few times, or was it about the same no matter how many times you press it?

Anytime the A/C is off, I have full brakes. With the A/C on, my foot goes almost to the floor, but braking does occur. But, I can pump the pedal with the A/C on and get better braking, and my foot goes to the floor much more slowly.

TheEmrys said:

Anytime the A/C is off, I have full brakes. With the A/C on, my foot goes almost to the floor, but braking does occur. But, I can pump the pedal with the A/C on and get better braking, and my foot goes to the floor much more slowly.

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I just dont get it, because even if the booster does not work at all, you still have brake, just harder to push. Maybe its because you need more force with the ac on due to the throttle boost with ac. I bet its your master cylinder. If you need tip on how bleed it/install, let me know. It's really easy. Cost me 10 bucks more for a new one compared to rebuilt at NAPA.

I have never had a car that the brake boost broke on.

Maybe the one way valve on the hose to the brake booster needs replacing. When you turn A/C on, it changes the RPM's a bit, which could affect how much air pressure is going through that valve. Just an idea off the top of my head.

I had a shop I trust look at it. They told me it was the master cylinder. So, I'll go buy one and pop it on. We'll see if that fixes it.

I would also lean toward a master cylinder.. when your a/c is going the engine runs a little hotter due to the extra work it's doing, as well as the heat being pulled off of your condenser... the master cylinder seals probably have a slight leak that is enhanced by the extra heat....
i think it's a safe bet to do one, just be sure to bench bleed it very thoroughly before putting it on the car, and then following the proper bleed procedure on all 4 wheels, this is very important to good brake performance. Air is bad for hydraulics.

-Henry

I changed out the Master Cylinder yesterday. Made all the difference in the world. Once all the fluid was flused out of there and the air bled out of the lines, it now brakes perfectly. Thanks for the help.