It’s my understanding that a partially clogged core, would cause there to be a temperature difference in the hoses. And I am not experiencing this issue. I used a pressurized hose to flush the core. In BOTH directions. I did get a bit of debris. But I kept going until I was getting clear water in both directions. “Seems” to be flowing through it… I don’t know.
You know, just because a 99-04 Cherokee is in the scrap yard, it doesn’t necessarily mean it’s for this issue. Its kind of a minor issue, as far as a reason to junk a vehicle.
If the cost of the repair is $1500 and the vehicle is worth, half of that, plenty of people will ditch the vehicle. I am not saying that ALL of them are in there for that reason. I know a couple of the guys who receive them in. This is the the most common issue. (Cost vs. value)
Are you talking the blend doors? see this? http://www.jgcparts.com/JeepHeater.html
Is you blower motor working in the lower positions when at idle?
When you lose heat in stop and go traffic, have you tried the blower motor in in its highest setting to see if heat is restored. If it is working in the lower settings at idle and you have tried the highest setting and it didn’t provide heat, then your battery, charging system and blower motor are good.
With the blower motor on high can you feel a good flow of air coming out the proper vents? You will need a good parts diagram to check the blend door but usually the linkage is external to the ducts and is visible from the bottom, if you know where to look. I don’t think this is your problem though because a stuck blend door would likely keep you from getting heat under all conditions.
You have already checked your heater core for flow so I think that is ruled out. Did you also check the heater hoses for flow. You may also have a bypass hose by the water pump to supply coolant to the heater core when the thermostat is closed, make sure it is not clogged up. Sometimes a pipe is used ot the bypass is molded into the block, water pump housing or gooseneck.
I believe your thermostat is good or you would get a check engine light for low coolant temperature. But I would question your coolant flow. To do this, you need to remove the thermostat when the engine is up to temperature. To do this safely, keep the engine running while you remove it and wear heavy rubber gloves and cover the cap with rags. Only turn the cap to the first indent until all the pressure is relieved, then remove the cap. Or you could remove the cap first and then warm up the engine.
Once the engine is up to temp and the thermostat is open, you should be able to see coolant flowing slowly in the top of the radiator. Rev the engine and the flow should increase, looking like the rapids on a river. If you are not getting a good active flow with the engine reved up or some flow at idle, you need a new water pump.
When the engine is running without the radiator cap, it over flows. I used a bleeder funnel yesterday and didn’t get any air bubbles.
I do not have dual climate controls. And Yes. I replaced the blend doors.
So what is the $1500 repair?
Seriously? I am making a general statement. I guess you can pick one.
I am always careful when it comes to animals and the environment. No worries. I always clean up any spills and dispose of the fluids in a legal way. 
I would test for exhaust gasses in the coolant.
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You know what you think is wrong, enlighten us. Sorry not blend doors, my best guess.
If the water pump were the problem, wouldn’t I have overheating problems? Because I don’t. It doesn’t overheat at all. I don’t have any leaks. My coolant level is constant in the overflow tank. And I haven’t had to add coolant. This thing has me totally perplexed!
With everything else on the cooling system working, there are only 2 possibilities for no heat from the heater,
- Partially plugged heater core. A heater core that is 75% plugged can still flow more water than the avg. garden hose can put out, so it would appear not plugged, if that was your test.
- Blend door.
I have stated a couple times previously, I have already replaced the blend doors. So, those are completely out of the equation. I guess, once I have more than a couple hours of 40° weather, I will flush it again. But all hoses are at temp. And there is flow throught the system. I’m just completely frustrated and at a loss.
Welcome to car repair. When absolutely everything is checked, and you are completely sure that you have covered all the bases, it’s time to start over. Deal with this car just like you’ve never seen it before and start from scratch. You will find your mistake or discover a base that you totally missed.
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Great advice! Thank you. I will try that for sure.
Like maybe the blend doors are not working properlY?
Are you consistently getting heat out of the defroster vents even when no heat at mid or lower locations?
Yes. The fan operates in every position from low to high. And in all vent locations as well. Now, if I place it on recirculation, it gets fairly warm and maintains a low but decent heat. Otherwise, I only get a trickle of heat through the defrost while at highway speeds. (65 and above.)