94 Accord EX brake problem

This may sound crazy but I have a 94 Accord EX Coupe that I have had for about a year now and when the a/c has been running for a little while I go to hit the brakes and the pedal will go to the floor, I was told last year that I had a master cylinder going bad but this does not happen in the winter when I don't use the a/c or when I turn the a/c off. Has anyone ever heard of this and if so what is causing it? Thanks

The master cylinder is going bad. You should have done it a year ago. Replace it before you kill yourself or someone else.

Thanks take care of it today!