2016 JKU owner with 50k miles. I'd been smelling coolant but could find no leaks. Replaced thermostat just to be sure. The smell seemed to go away but now, after a few weeks, I have no heat. Coolant reservoir is full, radiator is full, coolant temp sensor and guage warms properly. Blower is working, just no heat. I'm thinking it could be the actuator or blower door gear has gone bad. What am I missing?

 

I wonder if you've got casting sand blocking your heater core. My other, more hopeful thought is that you've just got a large amount of air in the system. Bleed the air and you're set.

 

I've heard casting sand issues in some JK 3.6 models. I hope that's not the case. Gonna burp it a few times to see if that helps. Thank you!

 

I park the nose up pretty high and run the heat. Tap that upper hose and give it a squeeze to see if you can get it to burp.

As far as the sand- you can verify by checking the bottom of your coolant reservoir. If it's there, it's likely in the system. I try to flush out the reservoir when I can to pull the sand out if it accumulates there. They sell a filter kit somewhere online to help pull it all out.

 

I doubt casting sand... It took 4 Burps - over multiple days to clear the air. Be sure to elevate the front when Burping, that was the difference from the 1st 3. NOW have you felt both hoses into and out of the heater core? Both should be hot.(careful). Also a certified tech tipped me on air check .. is the top rad hose soft and mushy COLD.. then check the bottom hose it should not be soft and mushy.. if so AIR in system. Good Luck.. This is not a promotion for DH but You might find this video interesing on flushing the heater core:

 

Unfortunately, I've become the forum heater expert over the years. A clogged heater core is possible but the hardest to diagnose where it's best to start with eliminating everything else until there's nothing left except for the heater core.

Start by burping the system with the front end raised as suggested. Air always travels to the highest point, so you're trying to get the mouth of the radiator up higher than everything else when you're doing this. Then fill with coolant and while filling squeeze the upper hose to assist in pushing out any air that may be trapped.

Having a radiator pressure tool can be a big help in diagnosing any leaks in the system. The radiators in the JK have plastic end caps. What usually happens when you're sitting still is that the radiator isn't hot enough and those end caps seal up, but as you drive they get hot and expand, but the leak tends to drip into the front lower air dam or skid plate and blow out while driving, so you don't notice much leaking of coolant on the ground when parked. With that said, the radiator leaking from the end caps has been a common problem on the JK for heater related problems. A radiator pressure tool helps to put the radiator under pressure to expand the end caps and expose those hidden end cap leaks when parked.

The JK also has a self burping system. So fill, drive, and then come back in a couple days and check the level of the coolant and top off. Do that for at least a week until you make sure there's no more room to fill for a few days straight. Also make sure the overflow reservoir is filled.

The trim door is pretty simple to diagnose by ear. Switch the temp dial from hot to cold very quickly with your ear placed next to the left center vent. You should be able to hear a seal/suction kind of noise of the door opening and closing when spinning the temp dial back and forth. I was able to put a camera snake down that same vent, feed it to the left toward driver side and see the blend door open and close when moving the temp dial. So if you have a camera snake, that may be worth while as well to visually confirm if the blend door is operating properly. The gear on the blend door has been known to strip, but in my opinion, that's the least likely cause of heat related problems.

 

SOLVED! After checking and re-checking everything, I kept feeling like it was the blend door actuator, and it was. But replacing it was a bitch! It's located under the dash to the right of the steering column. Not an easy fix, but that solved the problem. If you ever try this yourself, take a picture of where the actuator arm is located adjacent to the track it runs on. When that arm moves up or down, it runs along that track to open or close the blend door (allowing heat or cold to pass through). I made the mistake of NOT taking a picture of it, and even though it says it's a "self-calibrating" actuator, you still have to set it right. The YouTube videos I watched beforehand made this sound simple. Don't believe it!

 

Thanks for the follow-up! Glad you got it resolved.

 

Is this where that actuator is supposed to be?

 

I have a 2017 JKU Rubicon Recon. Just under 30k miles. This summer I replaced the battery. The A/C light, not the rear defroster light, would flash for several seconds before blowing cold air. Before the new battery, the A/C would kick in instantly when the knob was turned on. Also, the heater adjustment knob no longer worked. I figured that the new battery somehow fried the electronics in the heat adjustment dial. I pulled the panel out for the proper part number and when I put it back, nothing worked. Ordered a new three dial panel from Mopar, installed it, everything works again except the heat adjustment. I have a hard time thinking that both blend doors would go out at the same time when the battery was replaced. Most others report hot air on at least one side indicating only one blend door went bad. I guess because of COVID, I can't get a Jeep dealer to take it in to trouble shoot the problem. Both heater hoses at the top of the firewall are hot as well as under the dashboard. So I don't think it is a heater core or burp issue. I guess I could replace the blend door actuator by the driver's knee next. Any thoughts or advice is greatly appreciated.

Thanks