Automotive Air Conditioning Information Forum

Hello everyone,

I would like to know what would be the effects/downsides of adding a second evap core to my 95 Jeep Wrangler. I know this seems like a strange thing to ask as the evap housing will need modified etc., and they sell aftermarket AC's and stuff, but adding a second core is really the only feasible modification I can do. If it's too dumb of an idea then I will simply not do it, and stick with the one core. However, I am OK with the cost and general modifications required so the only question is effectiveness and other necessary changes to the system.

In general, I have heard that the positive effect would be minimal unless I also changed out the compressor and condenser. However, the main thing to remember is that I want to install them, not so that I have twice the frontal area, but so that I effectively have a core that is twice as thick. I am curious if that change alone would provide significant benefit.

Questions:

• Would putting the evap coils in series (relative to the airflow) give the intended effect of increasing the overall effectiveness of the A/C system? In other words the duct cross section is the same, but with twice the overall core thickness. If so, I would assume the coils should be plumbed in series in an arrangement where the coil next to the capillary tube is the one that the air hits second. (i.e. a "counterflow" arrangement as is typical in heat exchangers).
• I would have to increase the mass of the refrigerant charge when refilling it, right? How should that number be figured? In proportion to the volume of the system relative to the initial system volume, or is it more complicated than that?

Thanks everyone, I will check back shortly.

I never tried doing what you're suggesting. It might work, or it might not.

At a minimum, it seems to me that the TXV would have to be changed to a higher capacity unit, maybe the compressor and/or condenser, and also the refrigerant amount increased, as you suggest.

There is no specific formula for any of this, so you'll be experimenting on your own and modifying a system that probably took a lot of time and effort for the manufacturer to get just right.

Why modify an OEM system to begin with? Insufficient cooling?

Cooling is achieved when the refrigerant changes from a liquid to gas form in the evaporator. Since the refrigerant is already in the gaseous phase in the evaporator, so a second evaporator in series would seem to be useless. At least that's how I understand things.

Depending on the size of the second evap core, would you restrict airflow, creating an even bigger issue? If more cooling is needed, put a rear unit in the back before adapting a second core in a series.

Thanks everyone. Good points all around.

Think I will leave it stock.

Do you have trouble with the system cooling sufficiently? If so, we'll likely be able to help with that.

JohnHere wrote: Tue Dec 31, 2024 5:33 pm Do you have trouble with the system cooling sufficiently? If so, we'll likely be able to help with that.

Hi John,

What do you have in mind?

Subjectively, there is no rule of thumb when it comes to cooling and one's personal comfort level. But in my humble opinion, if the A/C in your vehicle isn't producing center vent temperatures at least in the low-40°F range at an ambient temperature of 80°F, then I would suspect some kind of systemic issue.

The outsized photo (multiple attempts at reducing it didn't work) shows the center vent temperature last summer in my 2018 Toyota Highlander (R-134a) on a 90°F-plus day in the humid South. I'm quite happy with its performance.