When I drive with the AC on my brake pedal has no pressure what so ever and you have to step on it hard for the brakes to kick in. But when I double pump my brakes the pressure comes back. This only happens when I am running my AC. Was wondering if anyone has experienced this problem. Thanks in advance!

 

You know there's no relationship between the AC and the braking system, right? The only thing I can think of that links them is the engine RPM. When you turn on the AC at idle, the computer will raise the RPMs a bit, and that will change the manifold vacuum, which powers the brake booster.

What's funny is that I swear I used to have the same symptom with my '95 (w/o ABS). It got worse over time, and eventually would happen whenever it was hot outside, regardless of the AC. I replaced the master cylinder, 'cause all the signs pointed to leaky seals, and now everything works great. I think the heat had been causing the MC parts to expand at different rates or something, and allowing the marginal seals to leak.

 

Tail... I have a 1995 Accord DX sedan (without ABS), and I have experienced exactly the same problem. It is intermittent, but I have definitely applied pressure to my brakes with my air conditioner running and had my foot float down on top of a spongy brake pedal. I am fairly certain I have only had this happen to me during warm weather with the air conditioner running. Pumping the pedal immediately restores good braking but the problem adds an unpleasant sense of peril to one's driving. I suppose I will get a rebuilt master cylinder since that seems to be the most logical approach to making the problem go away. Hope you haven't crashed into anything with your car during the lapse of time since your original post.

-- 1995 Accord DX sedan, 5 speed --

 

New master cylinder! Same happened to me. I fixed it myself.