Driving to work this morning in this 0* Colorado weather, the heater just died suddenly. Checked the blower motor fuse under the hood and it’s all good. Had no issues with different fan speeds, did have a problem where the only vents that worked were the floor and defroster dash vents though.

I have read that it could be the relay, could be the resistor, and could be the blower motor itself. My question is where to start based on not really having any issues and it just completely died out of no where.

 

So if you had no issues with different fan speeds, it shouldn't be the blower motor. I have a similar issue with the selector switch not blowing air where I tell it to like the floor, or vents or whatever, but I still have heat, although not as hot as it should be. The resistor is only about $12 at autozone. I'd like to hear opinion on the "relay" and if that causes heater door to open or close....
So are you saying the blower motor still spins, but just no hot air coming out anywhere? if thats the case, sounds like the blend door to me. hot side is closed. But dont ask me how to fix it. I'm going to wait on someone else to answer so i can check mine out as well hahahaha....

 

The vent/floor/defrost function is vacuum controlled. There is most likely a small vacuum line that is not hooked up somewhere on the intake manifold.

 

There may be some confusion here on your symptom. My take is that your heater blower motor completely died and is not running. No operation whatsoever. Is this correct? Or does the blower motor run but no heat in the cab?

If the blower motor is completely dead, I'd first try swapping the blower motor relay with another one of the same part number. I can't recall off hand for sure if there is a relay and I don't have my documentation in front of me, but I think there is a relay located behind the glove box (near the resistor block) for later model XJs like your 2001; I don't think early XJs had a blower relay.

If that doesn't work, then try temporarily hard-wiring the blower motor directly from the battery with some wire. That is a simple test that will tell you definitively if your motor is good or not and if it runs when hardwired, then you have an issue with either wiring or control electronics other than the fuse or relay.

 

I feel like by the description, he had no issues with different fan speeds, but the heat quit blowing... so maybe he lost the vacuum for the door and the heat side doesn't open anymore.... which may be close to my issue. My door is like opening partially so I only get warm air, not hot.