Questions and Answers

Honda Accord A/C On, Brakes Go Off Q. I have a 1991 Honda Accord EX with 168,345 miles. Every time I run the A/C on hot days the brake pressure will fail on the brake pedal; it will go all the way to the floor. If I turn the A/C off it will not happen. Any Auto Tech I have brought it to cannot figure out the problem. Thank you in advance for your assistance. Rob

A. I hate to say this Rob, but you got me on this one. There is nothing these two systems have in common. The only thing that I thought of, and it's just a wild guess, is there is a problem in the vacuum circuit.

Normally when vacuum is lost, however, the brake pedal gets very hard. Check the vacuum line routings and wiring harnesses and make sure they are routed properly. Then try pinching off the vacuum line at the brake booster and see what happens.

Other than that, I don't know what to tell you. I'm sorry.

Added 10/20/2005:

Vince, I am a former ASE Master Tech replying to the previous posting about the 1991 Honda Accord. I have a 1990 Honda Accord EX, 2.0 liter, 5 speed with 263,000 miles and had the same problem with the brake pedal going to the floor. The problem would occur only when very hot and high humidity which is the only time I run the A/C. I don't think the problem is having the A/C on but the high heat and humidity.

As you state vacuum/booster problems would make the brake pedal harder to depress. Given no external leaks and the brake fluid level staying the same my diagnosis was a bad master cylinder (internally bypassing fluid) and/or excessive moisture in the brake fluid. I replaced the master cylinder with a Honda OEM part (always use OEM) and changed the brake fluid. Problem solved. A Honda master cylinder is about $75.00 through Manchester Honda.

Jim
Laurel, MD