There have been a few posts similar to this, but haven't really found a clear diagnosis. I've got a '14 JKU Sport with 40k. I live in SoCal, so using the heater is rarely a concern unless I make a trip up to the mountains or sometimes when it dips into the 40's.

I've noticed that on occasion, I won't be getting heat from the driver side. But this will resolve when I start driving or get on the freeway. I'll immediately notice I'm getting hot air blowing on all vents. It seems to be only when I'm idling in traffic.

I've heard sometimes there can be a clog in the line, but hesitate to do a flush as I've heard this sometimes causes more headaches than solves. I've also heard about a blend door, but that it's a challenge to get to. Curious what ya'll think....

Again, it's not a major concern at this point. If I can fix it easily, great. I just don't want to open Pandora's box.,

 

I suspect you have restricted coolant flow through the heater core or the engine is running below operating temps. Have you checked the engine temps while driving? You can scroll through the menu options and get a digital temp reading.

Here' me flushing my heater core, it's simple and easy to perform.

 

I agree with flushing the heater core. But first, you might have an air pocket in your coolant. With the engine running, give the upper radiator hose a few squeezes. You should be able to tell if it's fluid or air. Check your coolant level to see if it goes down. Top it off and repeat. This is how I fixed a similar issue on my daughter's Liberty and the issue has not returned. I learned this after doing a search similar to yours and someone suggested "massaging" the hose. LOL. Good luck.

 

Yep, forgot about that, low coolant level will cause this issue as well.

 

To me it just sounds like low coolant level.

Could be just low coolant, could be blend door, could be partially clogged heater core (I don't think so though).

To rule out clogged heater core, When you have time, crawl under the front of the Jeep with a good bright flash light. If you have the sand in the cooling system issue, there will be sand in the bottom of the coolant overflow reservoir. With a flash light you can tell, as light will pass through coolant, but not sand, I deleted my pictures already, but it's pretty obvious if you shine a light on the bottom of the overflow tank.

If you do, you will need to flush, and likely replace the heater core. Look into the 30 min. Heater core replacement, it works, just make sure you use spring (constant pressure) clamps, and not hose clamps, or you will have leaks.