I'm having a similar issue. 2001 XJ. No hot air but dials work on dash to change from windshield, feet, face vents, etc. Removed glove box and looked under dash to find blend mechanism. It works when I turn dash dial from got to cold and back. I see it turning the mechanism and for a moment I had warm air on red and cool air on blue. Lasted for a day then back to nothing.
I removed both heater core hoses from the water pump area and flushed both ways with a water hose. I had good flow both directions. I hooked everything back up but left "water out" hose off and it shot out hot water fine. Hooked everything back up and warm for a day but not now.
I had been noticing that all summer when running the A/C and sitting idle I could here a click in engine compartment and the engine would change idle. I figured it was the A/C compressor kicking in, but it changes about every 15-20 seconds. I thought that was a bit too often but whatever? A/C was decent but at high speeds goes hot.
Now I've noticed that this still happens when the A/C is suppose to be off and the heater is on? Why would compressor kick in for heat? Or am I hearing something completely different than A/C compressor?
Air blows everywhere the dash dial is set to. It's just room temperature (cold right now). Could this be a switch issue that's engaging the A/C when it should be activating heat? Why did I have heat for a day and then none?
Hopefully something about mine will help TheBlueXJ?