This might be a bit of departure from the usual questions, but I figure a lot of y'all are accustomed to piecing together AC parts for your swap projects, so maybe y'all can guide me here.

I'm working on an L92/4L80 swap in my Buick Roadmaster Wagon. My boy Midnight (lab/chow mix) goes just about everywhere with us, but these wagons didn't come with rear AC, and on hotter days in GA/SC I worry about keeping my buddy cool.

I've been wanting to add a second evaporator to the rear of the car. Something that'll fit in one of the rear fender storage areas. The evaporator mounting/wiring I can wrap my head around, but what about

• Condenser sizing
  • I'm guess as much surface area as possible is the trick?
• Compressor selection
  • Not sure how much flexibility I've got here or even if it matters?
• AC line routing
  • Am I over thinking this, or is it as simple as wye-ing the high and low side hoses after all other inline hose parts. Basically, wye the lines after the orifice tube and before the the accumulator?
• Are there any other parts considerations for a system with two evaporators?

Any insight would be appreciated!

 

Take a look at the Chevy Suburban layout. You can see what is used for compressor and evaporator sizes.
Some "creative piping" and it's a "cool deal".
Fido will thank u!
My 02 1500 rear air will give you frostbite!

 

As suggested you could reference the layout from a Suburban rear auxiliary setup. OE auxiliary evaporator cases are generally really large and ugly. Always hidden under panels. If you have that option that's good. However... companies like Vintage Air have some compact evap cases that could work and don't necessarily have to be hidden. There are similar aftermarket cases for cheap on Ebay and Amazon as well.

The compressor that's on you vehicle now is likely more then good enough to push a modest auxiliary evaporator. The little compressors that come on subcompact cars are probably the only ones that can't do it.

You want the largest condenser that will fit behind the grill. More importantly you want to pull as much air through the condenser as is mechanically possible. If you have a mechanical fan then I would recommend adding an electric condenser fan that comes on when the ac is on. If you think you can upgrade the condenser to something larger try to use a modern parallel flow type. They're much more efficient then the older serpentine and dog leg condensers.

The lines going back to the auxiliary evaporator are fairly straightforward. You want to tee off from the liquid line. That's the line going from your condenser to your expansion valve/evaporator. That rear liquid line will go to your new rear expansion valve/evaporator. You also have to tee off from your suction line. That's the big one from the evaporator to your compressor. Make sure neither of the lines are touching anything hot like exhaust or rubbing against sharp edges. I generally insulate the lines with thermo sleeve if they're in close proximity to exhaust.

Obviously the R134 capacity of your system will increase with the new lines and evaporator. Once you get it together take it to a shop that does ac work and have them evacuate and charge the system. Let them know what you did so they can accurately adjust for the higher capacity. They should run the system to check pressures and performance.

For what it's worth I'm the lead ac tech for an ac specialty shop in the Denver area. I service, repair and install air conditioning for most vehicles.

 

Don't overlook conversion van rear units.

 

Absolutely killer response, bossman. Thanks for sharing your expertise. I've been eying some of those small aftermarket evaporators. Just need to start measuring and figuring out what can fit. Hopefully I can update this thread in a few months when I make some progress.

 

I just noticed you mentioned the orifice tube and accumulator. I must have read over that. For the liquid line to the rear expansion valve/evaporator you tee off the line between the condenser and orifice tube. In the rare occasion that the orifice tube is in the condenser you're going to have to make some major changes. Your rear evaporator needs it's own expansion valve. There are some auxiliary evaporators that use a CCOT with an orifice tube but you can use both types in a dual system without issue. Apologies for any confusion.

As for the suction line, most accumulators are on the firewall right at the evaporator. You can tee in your rear suction line between the accumulator and the compressor. If you have a bunch of line between the evaporator and the accumulator you can tee in there if it's more convenient.

The liquid line to your rear evaporator will be a #6. The suction line will be a #10. If you're doing the work yourself grab a bottle of PAG oil without dye to oil all o-rings during assembly. I also put some PAG oil on the threads of any threaded fittings. Helps prevent corrosion and grief if you have to remove them later.

 

Not a bad option if you can find one in decent shape. Worth looking into. Also newer Ford passenger vans (E250, E350) have floor mount auxiliary HVAC cases that are fairly compact. Probably better luck finding one in good condition over the aging conversion vans.

 

Glad to assist. Thankfully there are a lot of evaporator options from very modest to ridiculous. Shouldn't take you long to find what will work best for your setup.

Don't forget to plan for a case drain. You see a lot of humidity in SC/GA. If your evaporator case is in the cabin you need to have a drain tube or two to let the condensation drain out.

 

That and insulate the suction lines and the expansion valve going into the rear unit. Moisture will build up and drip off them. Dumb dumb works really well for insulating the metal fittings.

 

Also a good idea.

 

I'm always looking for "tricks of the trade." What is this "dumb dumb" that you've mentioned? I tried to look it up on the internet but I came up empty.

 

Dumdum is a sealing putty. Very easy to use....

 

That putty tape will work but it's sort of fragile. The stuff that is used most commonly is known as "tacky tape". I think the more official name is PresTite Cork Tape. It's also referred to as expansion valve insulation tape or tacky cork tape. It works good just make sure you compress it around the expansion valve and other joined metal parts as tight as possible. Don't leave any air gaps. It's so sticky it has to be made from pure evil dipped in cancer.

 

Greg and Kill Box, thank you for the explanation of what it is. I was able to find this:

PresTite Tacky Tar Cork Expansion Valve Tape 1/8" x 2" x 30' FT

 

You're welcome!