I have replaced the master cylinder on my 2006 chrysler town and country about every week we keep losing brake pedal so we have bleed them and get pedal back. the only place i find air is the front driver wheel.

Could be a couple of problems, bad master cylinder (not bench bled properly or bad seal out of the box, I have had a few like that), proportioning valve seal, brake line not tight/sealed properly sucking air into system,bad caliper. First of all, are you losing brake fluid along with your pedal? Need to know that first. If you are, try to find where you losing it from, you will find your problem. There can be absolutly NO leaks in a brake/hydraulic system. If not, check that all lines are tightly seated and nuts are quite tight using a line wrench to get proper torque. If so, you can replace the master cylinder again (take old one back to store for new one under warranty) and be sure to thoroughly bench bleed. When bench bleeding, take your time, do not push plunger in too quickly, use a SLOW steady push until ALL bubbles, no matter how small have been eliminated. Tapping on the bottom of the cylinder while bleeding will help remove trapped air. Even a very small amount of air will take forever to bleed out at the calipers. If cylinder/all calipers/lines appear to be right, I would suspect the proportioning valve is faulty. To find it, follow brake lines from master cylinder to where they go into the valve. Replace. Hope that helps.