Blows cold air only

[lloydrage]

Hello. I need some help. 2022 JLUR diesel. The heater no longer works. It only blows cool air. Ac works great. I’ve tested different settings and it didn’t change. Verified thermostat opens and blender door actuator works.
I also flushed the heater core today but no improvement. Coolant level is correct.
What could I be missing?

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[mwilk012]

Well, if all of the things you posted are true, the heater would work. The question is, which one are you wrong about? How did you check each of these details?

 

[lloydrage]

does flushing guarantee heat core works or is it possible even if you flush it doesn’t?
Bold to say everything I’m saying isn’t accurate

 

[lloydrage]

Thermostat was tested by checking upper radiator hose got hot once more hit temp.

coolant level was checked by checking overfill reservoir.

heater core was flushed by disconnect hoses. Hooking water hose and compressor. Some sand / debris came out but not much.

Blend door actuator was tested by removing glove box. Adjust settings and watching it move.

 

[mwilk012]

If able, measure the temperature of the heater core pipes, either by feel or by actual temp. Odds are good that heater core is mostly clogged if these conditions are accurate. Were you able to get full hose flow out of the heater core?

 

[alphawolff]

does flushing guarantee heat core works or is it possible even if you flush it doesn’t?
Bold to say everything I’m saying isn’t accurate

You cannot flush a radiator (heater core). I'm not sure where this falsehood was originally presented, but it doesn't work. You can clean out old fluid, but you cannot clean out an obstruction.

Imagine you have one inlet, one outlet, and four separate lanes connecting the two. If you put water into the inlet, it'll flow evenly between all four lanes. If you block one lane, the pressure will simply increase on the other three lanes to compensate. This is effectively how radiators are designed. If your obstruction is soluble it's possible to get it to de-clog, but it's difficult and requires certain types of cleaners.

That being said use a digital thermometer on your heater core hoses. There's either a clogged heater core or your HVAC actuators are not functioning correctly. The driver side blend door actuator fails routinely, and is probably the issue here. You can pull it off and operate the blend door manually to verify.


FWIW this is why if you have oil mixed into your coolant you need to replace everything. Engine, heater core, radiator, oil/water coolers, etc. You'll never be able to flush it all out.

 

[Old Dogger]

Blend door actuator was tested by removing glove box. Adjust settings and watching it move.

Our Wrangles have three (3) Blend doors. Starting from driver side to passenger side. The Blend door on the driver's side controls the heat and cold temperature settings. The center Blend door controls the air flow through the ducting. The one behind the glove box, controls the outside air intake, or rec-circulate. So, you need to be checking the Blend door on the driver's side.FYI

 

[mwilk012]

Our Wrangles have three (3) Blend doors. Starting from driver side to passenger side. The Blend door on the driver's side controls the heat and cold temperature settings. The center Blend door controls the air flow through the ducting. The one behind the glove box, controls the outside air intake, or rec-circulate. So, you need to be checking the Blend door on the driver's side.FYI

Those other doors are by definition not blend doors. The temperature blend door is so named because it blends hot and cold air to achieve a temperature. The recirculation door controls recirc function, and the mode door controls mode selection. On some vehicles you’ll have a separate defrost door actuator.

Op, do you have dual zone heat or single ?

 

[lloydrage]

I have dual but both sides are same issue.
Also update.


Okay got the driver side off. Tested and it moves both ways. That bugger was tight to get to.
So I guess I go back to what alphawolff says. I didn’t realize you can’t flush the heater core. So it’s gotta be that. I checked hoses and they get hot.

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