I have a '99 K2500 Suburban with 150k. It has the rear seat heat and A/C option, which works great. However, it has a strange problem with the front A/C - the front A/C only blows cool air when the rear A/C is turned on. The rear A/C always blows nice cold air whenever it is turned on. But the front A/C basically doesn't get cold hardly at all if the rear A/C is turned off, but it does get cooler when I turn the rear A/C on. I'm not sure what would cause this, as the front and rear A/C have separate evaporators. I was thinking maybe the front evaporator may be dirty, but that wouldn't explain why it gets cooler when the rear A/C is turned on, since the rear has its own evaporator in the back. Does the front and rear A/C have separate freon circuits, or are they on the same loop? If they have separate circuits, maybe the front is low on freon. But if they are on the same circuit, I would have no idea why the front blows warm. Any ideas? Thanks!