Drvrs side blows cold, pass side blows warm even on high. No dual temp on truck.

What is your question?

The truck blows super cold on the drivers side, but blows warm on the passenger side. What gives? I dont have dual air temps...just the normal stuff. I've only made one modification to the truck and added a K&N cold air intake. Any ideas before I drop some $$$ at a shop? Please, no smarts remarks...just some good advice. Thanks everyone!!