Brakes very strange

[2000VFR]

My wife has a 94 pickup, no abs. For some reason the back drivers side brake just locks up while driving down the road, might be both back brakes but seems more toward the drivers side. When this happens the brake pedal it's self becomes impossible to push. Now for the strange part, it ONLY happens when the air conditioner is running. I've had the brakes inspected and adjusted to no avail. Does this sound like a vacuum system problem? I'm stumped if anyone has any ideas please throw them out there anything is possible at this point. Thanks in advance.

7-16-09 UPDATE: For the first time, today it locked up without the AC running. Taking it tomorrow to get the wheel cylinders checked. Still up for ideas if anyone has them.

[fasttoyotapu]

The brake and A/C systems are not conected in any way. It sounds like to me that one of your wheel cylinders is siezing up. you may want to check that out before it becomes a bigger problem. I also recomend a brake fluid flush to asure that your brake fluid does not have any water in the system which could cause a your brake system to act up.

now with your break pedal feeling hard as a brick... your a/c system puts quite a strain on your engine. if you have a vacuum leak, your brake booster may not have enough vacuum to help you out. again a brake flush would rule out any contaminates in your brake lines / master cylinder.

I would also check out your brake lines to rule out any kinks in the system which would cause a slugish wheel cylinder.