Heater Core vs Blend Door

I've posted in past threads about my '99XJ not getting warm anymore (just enough to be comfortable with a coat on), but I wanted to start a new topic for a specific question.

How can I troubleshoot or test if the above issue is actually the heater core or a blend door issue. Is there a way to rule out one over the other so I'm not trying to chase two issues at once.

I have the same quetion for my 99 Cherokee Classic. Core vs. Blend Door. How to test?

From what i have seen, its most likely a heater core that has some gunk in it. There is a better thread on the topic on page 2 right now of this section, or go to youtube and search for eric the carguys 4.0 heater core video.

Run the Jeep with the fan off until it's up to temp. and then feel the hoses where they attach to the heater core at the firewall. If one is warm and one is hot, like mine:tear:, it's probably because the core is plugged.