How do I upgrade my climate control system?

You are in for a major project. The best approach, and not a good one, is to find a donor car in the salvage yard because you're going to be making numerous trips. The entire heater box is different with different actuators. The dual zone gimmick requires the use of an unreliable, complicated computer. Every manufacturer has trouble with their versions of these systems.

I'd like to say you just need to transplant a few parts and it will work, but the truth is there are unexpected things you're going to run into. I helped a friend rebuild a 2006 Dodge dually diesel truck a few years ago that was crashed so severely the engine got pushed back a foot and crushed the firewall and heater box. My job was to take a used normal one and rebuild it to make it into a dual zone to simply match what came in the truck, and that was a very time-consuming ordeal that involved cutting plastic, forming custom runners, and transplanting actuators. We agreed we would never attempt that again. He had a couple of parts trucks that we got the heater box from, but if we ever have to do that again we're going to search for the right box to match what the vehicle came with.

I can pretty much guarantee at some point you're going to give up and cobble something to make it work "good enough". I also watched a coworker take the entire air conditioning system off a brand new van and try to put it into a different one that a customer wanted to buy. That involved cutting and transplanting part of the firewall in our dealer's body shop, upgrading the suspension just as they do at the factory to hold the additional weight, and lots of other modifications, and that was in the late '90s when those vans didn't need silly computers to do what they do today. He spent over two weeks on that project and it looked like crp when he got done. Sure, it worked, but everyone lost their shirt on the job. We all would have been better off selling the customer the original AC-equipped van and repainting it to the color he wanted.

Maybe I misunderstood something. What do you mean by "outside temperature"?

Oh; I get you. I have two minivans with a temperature sensor in front of the radiator too but mine are for the overhead compass / thermometer. If what you're describing is for the heater / AC system, that is not REQUIRED for the dual zone to work. It would be one of the features of it. The thinking is if the computer knows the temperature of the air hitting the AC condenser and what's coming into the car, it can adjust how hard the AC system is working rather than wait for the temperature sensor in the heater box to be affected by any changes. Just gives it a little more control. Chrysler has some cars with a photo cell on top of the dash called a "sun load" sensor that kind of does the same thing. If sun hits the dash, the computer decides for you to blow more cooled air in your face.

Your ambient air temp sensor might be the same one used with automatic temperature control and single zone. That is another can of worms. When I worked for a very nice Chrysler dealership in the '90s and found out they were discontinuing the Dynasty, I ordered one the last month of production and got every single option available, ... Except automatic temperature control. I saw how many of those systems my coworker, the AC expert, was repairing on relatively new cars and trade-ins of other brands. Later, my sarcastic response to my students was "I'm pretty smart; I know how to push buttons and only I know when I'm too hot or too cold, so I don't need a complicated, unreliable computer doing that for me". Some days I'm hot at 65 degrees and some days I'm cold at 75. That silly computer doesn't know so I still have to reach way over to the middle of the dash to twiddle an adjustment.

Anyway, it's not that you can't transplant the system. It's that I know you'll be in for lots of frustration. The systems I've worked on before are limited too in how much difference there can be from one side to the other because there is still just one heater core and one AC evaporator. Six to eight degrees difference is about it. Both of my Caravans have rear AC and heat which gives you a REAL wide range of temperatures, but the rear passengers rarely fiddle with it or bother to make adjustments. I think once the novelty wears off, there's not much point in even having it. The models newer than mine have the rear units in the REAR where I can see them having some value. Mine are right behind the driver's seat. Lot of good that does for the people way in back, but hey, it was a cool feature when we bought it.