Heat comes out driverside/cool air comes out the passenger side?
It sounds like your blend doors are broken. As it turns out, this is a VERY common problem with grand cherokees. My father and I fixed this problem on my 2001 Jeep Grand Cherokee Limited 4.7 about 2 months ago using a product called Heater Treater, found here: http://www.heatertreater.net/
You can find a very helpful detailed write-up of the fix/installation here: http://www.jeepsunlimited.com/forums/showthread.php?t=854246
Trust me, this REALLY works and a lot of Jeep Grand Cherokee owners, including myself, have done this. YOU WON'T HAVE TO REMOVE YOUR DASHBOARD, as the repair is done by simply removing your glove box. The downside is that you will lose Dual Climate Control, as the driver side thermostat will now control both sides. For me, it was worth it. Only spending about $150 for a Do-It-Yourself solution, versus spending about $1000 to have a mechanic remove my dashboard to fix it.
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