My brakes on my 92 Accord normally work fine. When I have the AC on for about 15 mins of driving the pedal will go to the floor. If I turn off the AC the brakes will work fine after that. Any Ideas ?

 

It is very strange. You can call Honda directly and ask, but I would ask a local mechanic that you have used services in the past. It is almost rude to just ask a shop for question without intending to have your car serviced there or have never used their service in the past.

We here don't mind giving freebies, but I think mechanics like to make money while at work.

 

if your brake master cylinder has never been changed, then i suspect the seal is starting to go.

and the reason why it coincides with you using A/C might simply be because the engine runs hotter when the A/C is on. when my BMC started going, during hot days (90+ degrees), the pedal would sink. but 80s or lower, i could brake normally. but eventually, you'll completely lose the seal and you won't have any pedal pressure.

now you say when you turn the a/c off, the brakes work fine. you mean to tell me once you start losing pedal pressure and you turn off a/c, you regain pressure immediately? if that is the case (though i find it hard to believe), something else is screwy.

 

wow weird chit me being a newbie i would have never guess that the ac has anything to do with brakes damn i love old cars with no a/c well roll down the window

 

My wife's 91 Accord has the same problem. I will be changing the master cylinder very soon.

 

sounds like a vaccum problem or the brake booster itself (the large, black "housing" that the master cylinder is attached to) This is usually something better left to a "professional" as they have the nessecary equipment to test the vaccum and the booster.

 

This is definately a vacumm issue, sounds almost like the A/C is over boosting the vacumm. If you loose vacumm the pedal usually becomes rock hard.

If you don't know how to trouble shoot the vacumm lines a true service manual from www.helminc.com may help. Else have the local dealer or mechanic service it for you. It could be failed part on the brake booster but not always. Usually the bell goes but that creates no booster vacumm.

It could simply be a check valve but I haven't trouble shot the Accord system recently so I can't give you an exact solution.

Your engine creates lots of extra vacumm in the intake manifold, engineers have used this extra vacumm to run lots of features, power brakes and cruise control too. With the AC on does the cruise work?

 

http://www.mpbrakes.com/troubleshooting.htm

OK it may not definately be a vacuum issue but if it only occurs when you run the AC I highly expect it.

Check out the FAQ's at this link.
Plus they have a general how to diagnose your problem section.

This site hooked me up with brake parts for my dart (nobody made power brake dart parts) when I had it, they can custom make anything you need--for a price

 

I took my car in today. They said it is losing 4 lbs of vacuum pressure when they turn on the A/C. Which is causing the brakes not to work. He said the loss of vacuum pressure could be caused by the whole in my resonater and the valve cover was loose some oil was leaking and leaked in the spark plugs. I am going to just replace the resonater with a pipe and I tightened the valve cover about a year ago because it was loose and leaked some oil and I guess it needed to be tightened again. Any thoughts on the vacuum issue or how to keep the valve cover tight. They wanted $275 bucks to put a new valve cover gasket,plugs and wires. I am going to do it myself for a lot less.

 

They also said that Honda had a technical bulliten out on it. Anybody seen this or know where I can get a copy ?

Thanks