Heater only working on Driver side

I have the limited Jeep Grand Cherokee (1999) and my heater doesn't work for the passenger side of the vehicle.. only the driver side.. each side has separate controls and i'm unsure what would cause this? any ideas?

Sounds like the Blend Door issue, fairly common on JGCs equipped with the Dual Zone, Automatic temperature control.

Check for fault codes as described here-
http://www.wjjeeps.com/climate.htm

Operation and repair-
http://www.wjjeeps.com/hvac_sub_assembly.htm

i appreciate it.. unfortunately that seems like aton of work to make my passenger happy.. ha.. i might just have to put this fix on hold til the weather falls substantially..