Probably more of an issue for tech, but oh well, im feeling helpful.
If you arent having heat, and it is blowing cold air, check your temperature gauge. If its not pretty much in the happy middle around 195 mark, you are looking at a thermostat stuck open or possible non-existent depending on the IQ level of the previous owner.
If it is running at normal operating temperature, might want to check into flushing your heater core. Plenty of info on that topic using the search function.
I would only look into your blend doors if you can tell you are getting hot air SOMEWHERE but maybe it isnt getting to the right places. If its just blowing cold/cool-ish air then its more than likely a derivitive of the above scenarios.
- '99 XJ -
Lifted, Locked, Stiffened
July 2013 COTM