2018 Rebel 1500 Dual Zone heater core issue

[DuallyDean]

Several posts have similar symptoms; need confirmation troubleshooting is on the right track.
I have developed a small coolant leak at the back left head on the 5.7 (almost guarantee it is a head gasket). Trying to buy time I used a bottle of Blue Devil radiator and block stop leak. IMMEDIATELY THEREAFTER, I have lost heat on the driver's side vents, both when in floor and in dash mode. This is also true of the rear seat vents (driver side cold, passenger side hot). The truck has dual zone climate control.
Can someone explain in a nutshell how the HVAC system is configured? I have checked the "blend door" accessed by removing the glove box. It operates correctly thru the full range. Airflow is strong thru ALL vents when they should be active during their mode. It is a temperature problem ONLY on the driver side. Are there TWO heater cores, or TWO separate coolant feeds to a divided heater core to facilitate the dual zone system? Or is airflow divided over two different areas of a common heater core (top half/bottom half)?
I am fairly positive the introduction of the stop leak has caused my problem (and to add insult to injury, the head gasket leak is still there ) Other posts seem to indicate there are not 2 different blend doors to control temperature independently between driver and passenger side, but rather that the heater core plugs at the bottom and that's where the driver side air blows across. Both heater core hoses are hot, but as others have indicated that doesn't necessarily mean coolant is flowing thru the ENTIRE heater core. Am I looking at a driver side only blend door problem, or a partially blocked heater core?
I've pulled wrenches my entire life; but prior to buying this 2018 RAM, the last vehicles I bought were a 1994 Dodge 3500 Diesel and a 1994 Dodge 2500 Diesel. The 2018 Rebel just went out of warranty 15k ago, so this is the first I've had to troubleshoot anything "modern".

 

[nlambert182]

The core is in 2 "sections" (internally), with the driverside being fed from the bottom section. It's likely that the bottom half of the core is clogged, and would explain why you only have heat on the passenger side.

 

[DuallyDean]

Thank you for the response! Not what I wanted to hear, but what I kind of figured. I am going to try backflushing and hope I can get it to clear, but it sounds like that has been tried by others with only mixed results. I don't want to have to change a heater core, but if it comes to that, any good youtube tutorial links anyone wants to share?
P.S.-- it's currently +2 degrees F here in Minnesota this afternoon.

 

[mrack]

Motor city mechanic on YouTube has a 3 or 4 part series on changing the ac evaporator, it’s the same process.

Part 1/4: 2009-2015 Ram trucks A/C evaporator and recirculate housing

Please use the following link when ever using Amazon.com. Any purchases you make on Amazon will help support this channel.http://amzn.to/2mALgqSFeel the need...

m.youtube.com

 

[nlambert182]

I backflushed mine 5 times before giving up and sending it to the shop. I could get heat back for a little while but it never held. Maybe you'll have better results. I looked up what it took to replace it and decided it was a job I didn't want to tackle. It took the shop 3 days total.

If you want a ballpark just for gits and shiggles, it cost me about $1,900. That's labor and all OEM parts and included replacing the evap, the heater core, and all 5 actuator motors (a while we're in there thing). Best money I've spent in a long time.

 

[DuallyDean]

I asked at the stealership yesterday. Book says 5.5 hours, says it would be about $1,300.00. I'm sure that's a labor only estimate so $1,900.00 is right in the ballpark.
The insult is that it's going to be $1,200.00 to fix the original problem I was trying to avoid that got me here in the first place...the leaking head gasket.