hello and welcome to just answer.
the first thing to check would be the heater hoses at the firewall they should both be hot after the jeep is warmed up. there is no vacuum control valve on the newer chryslers like there was years ago. if the heater hoses are luke warm or cold then there is a restriction in the heater core and the heater will need flushed out with a garden hose.
Where will I find the hoses - it is kind of cramped under the hood and they are not readily visible?
give me a second and ill see if i can dig up a pic for you
ok i couldnt find a picture but the heater hoses should be in either the center of the firewall or towards the driver side right about the top of the motor, the hoses are 5/8 and if you cant reach them at the firewall follow them back towards the engine and you can feel them for warmth at the easiest spot to get to
How likely is it that the heater core is clogged, considering that the car is only seven years old and the coolant appears to be in good condition?
when you select hot or cold can you hear a change in the air coming from the vents?
No I cannot.
The control feels a bit loose. That is, there is pretty much no resistance when I turn it.
the reason i asked is it is possible that this could be an actuator that has failed or even a broken blend door in the housing. with the blower on you should here a change as you select hot or cold.
I will verify. Won't take long.
Air flow does change a bit and the sound quite a bit. I found the heater hoses. They are on the passenger side behind the coolant reservoir. Checked the coolant - it was way down. Did not think it could be that because the oil change shop checked it on Saturday. I am wondering if it did not drop suddenly the first time we used the heater - it seems we had some engine work done over the summer and when the shop replace the coolant, perhaps the heater was not turned on so the core would fill too. However you said there is no valve that turns on and off the heater coolant supply, and we have no water in the oil and not coolant puddles so I am wondering where it all went.
yeah i never thought to mention low coolant, i just assumed it was full.
definately get it up to level first and if you get heat back you may want to have it pressure checked for a leak.
Heat came back. Will monitor level and see how it goes. Will have pressure test if it drops again. Thank you.