Riptide9

The fact he has heat on one side but cold on the other seems to be clearly pointing to the blend door actuator imo

Suss1173

Turns out that I was low on coolant. I put about a 1/2 a gallon of distilled water in this morning and I let the system burp a bit and now the heat is blowing hot, and the aux fan isn't coming on either. However, I have a few symptoms that Rednroll mentioned in his prior post and in his thread. Unfortunately I probably have a slight leak someplace... Hence that is why it was low on coolant.

I bought the JKU 1 year old with 14K miles on it, so I cant say for sure the coolant has ever been mixed... But It currently has 47K and I haven't had to do anything other than basic maintance on it. Something else that leads me to think I have a slight leak, is that I have always noticed a slight whiff of coolant when I get out of the jeep. It doesn't matter if I was on a 2 mile ride or a 2 hour drive, as I walk to the front of the JKU I get a slight whiff of antifreeze (smells like maple syrup). I used to check the levels often and they were always OK, so after a while, I stopped checking. I also mentioned it to the stealership when it was still under warrantee. However, they didn't find anything, and I didn't demand a pressure test of the system (shame on me). I also notice some gurgling when I start it in the morning- Further indicating air in the hearer core, which I assume could be from a leak?

Based on my symptoms of slight smell of coolant toward the front of the jeep, the gurgling at start up, and now needing coolant, I should barrow a pressure tester and start there?

Riptide9

Weird, so how does that allow hot air on one side but cold on the other?? Anyone?

Suss1173

I have been trying to figure that out too. But I can say, that a little more water and bleeding out some air solved it for me, at least for now...

Rednroll

I had heat on one side and not the driver's side as well. So what makes it so clear about it pointing to the blend door? I confirmed my blend door was working.....go read my diagnostic thread, it's in there. If it's the blend door, I can make the same point...why is it only blowing cool air out one side since the blend door feeds all 4 of the vents?

Here's what is going on. If you take measurements of the air temp coming out of the front vents, which I have done, even when the heat is working normally, you will find that the driver's side vent will blow slightly cooler air than all the other vents. The 2 center vents will always blow the hottest. Why? I don't know for sure. It could be because of the further distance the air has to travel to each of those vents where the HC is located in the center of the dash, on the passenger's side. It could also be the way the duct work is set up in relation to the actual HC and how the fan is positioned to blow air across the heater core. Lots of practical reasons for it, it's a fan blowing air across a hot piece of metal with a thermal transfer of heat, the further that hot air travels away from the heater core, the cooler it gets.

In the case of either blockage or air within the HC, the entire area of the HC is no longer heating up. The HC is about 12inx8in in area. With any blockage or air being present inside of that 12x8 area, the actual area of the heating elements is getting reduced and the smaller the area being heated, the less heat/hot air that will get generated when the fan blows air across the HC. Pretty simple really, the smaller the HC...the less heat that can be produced inside of the vehicle. The driver's side vent is already blowing cooler air, and the cooler air becomes the coolest and most noticeable that it is not hot.

Rednroll

Your next step will be in determining the reason why your coolant was low. There's 2 common causes for this. 1. Radiator leak 2. Lower Intake Manifold gasket leak. The most common problem is a leaking radiator. The best way to confirm and find the leak is to use a radiator pressure tester. This is also in my diagnostics thread.

What typically happens is that the radiators will spring a small leak between the core and the end tanks. The problem is, that it won't leak unless the engine is running and getting hot because when the engine is cool, then the radiator doesn't have enough pressure in it which therefore doesn't cause the tanks to expand and expose the leak. It's typically a very small leak which shows its ugly head when you're driving down the highway and the coolant is blowing out onto the highway without you realizing it. Any of it that does drain out, gets caught by the air damn or skid plate, directly below the radiator and therefore you rarely ever see coolant dropping on the ground to notice the leak.

Riptide9

Very interesting info Rednroll. Thanks for this

Rednroll

Start by pulling the shroud off of the top of your radiator and look down the sides of each end tank of your radiator to see if you can visually notice any areas where it has been leaking coolant. Also, look on the air dam or skid plate, since that's where coolant typically drips down to...and not onto the ground.

I purchased the pressure tester from HF...I've only used it once since I've gotten. It did the job. You only want to pump the pressure up to 15psi. I noticed my end caps starting to leak once I got the pressure up to around 13-14psi.....so yeah, that radiator doesn't leak until it's up near full intended operating pressure.

Rednroll

I spent over a year diagnosing my heater problems.....and absolutely made sure to try everything before resorting to replacing the heater core. I learned quite a bit about our JK's heating system along the way, so I'm glad I can share, since I really needed the help back then, and understand how maddening this stuff can be to figure out.

cfarq

I had no heat on drivers side vent for about 3 years. I finally found a video about back flushing the heater core and i did this yesterday. My heater now works the best it ever has since owning the jeep. It gets extremely hot now. I would try this before anything else as its about a 20 min job max.

There are several videos on YouTube about this.