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Custom A/C system design

Xnke on Wed June 02, 2010 12:17 AM User is offline

Year: 1972
Make: Datsun
Model: 240Z
Engine Size: 2.9L
Refrigerant Type: R134a
Ambient Temp: None
Pressure Low: None
Pressure High: None
Country of Origin: United States

I am currently collecting parts for a custom A/C system in my resto-mod 240Z. I've done every inch of the work on the car myself, from body repair, to driveline rebuild and customization, to gutting and hand stitching my custom interior.

Originally, the USDM cars only had a dealer-installed suck-through system, and it froze up all the time and just generally didn't cool the car. My car came with one of these.

With the 1974 model year, the factory installed in-dash system came about, and worked acceptably. However, it will not fit behind my dash.

I am going to have to make a custom airbox, fit my brand new Everco R-12 tube-and-fin evaporator core (it looks like a multipass unit, three tubes in, three tubes out in parallel), and a heater core (still looking for something similar in size to match up to this evaporator) inside, and find a good blower to push air through it.

The compressor is a SD-508 clone, with Flare Type fittings on it. It is marked for R-12 Or R134a use, but has NEVER been used. it is not locked up, came with oil inside, and was manufactured in 1994. The fittings had sealing caps screwed onto them and the compressor was shrink-wrap-sealed.

The evap core is for a 1974-1978 car, so it should have enough capacity to cool the car. It has an expansion valve on it, with a tube that is bolted to one of the outlets of the evaporator. This evaporator has copper tubes, and the brass expansion valve is connected with flare style fittings. The fittings to connect this to the rest of the system are flare style fittings. This evaporator was new, still shrink-wrapped in the shipping box from the Nissan dealership. It has never been removed from the box before today, and I found it in the back of the car when I was cleaning it out after buying it.

I was hunting through the junkyard for a common parallel flow condenser that would fit the front end of my car and be easily obtained if a replacement is needed. I stumbled upon a condenser from a Mazda 626, marked for use with R134a and R-12. It's a parallel flow style, and fits just right infront of the radiator. This condenser measures 24" from endtank to endtank, and 16" top row to bottom row. It is 1/2" thick. On the top right side, it's got an aluminum line about a half inch in diameter, and on the bottom left, it has another about a quarter inch in diameter. This condenser is all aluminum, and has o-ring style fittings on it. I will probably need to cut these lines shorter, as they cross over infront of the evaporator, and braze in fittings that are better positioned for my car.

Looking down on the engine bay from the front of the car, right infront of the radiator:

Inline six engine bisects the engine bay into right and left halves.

Compressor is mounted in the Right Front of engine bay

Compressor Outlet would come forward through the core support to the condenser, pass through the condenser from the large-diameter line, then through the accumulator(?), through the core support, along Left Frame Rail and into the cabin in a small-diameter line.

Once inside the cabin, the small-diameter line would pass through the expansion valve, then through the core, exiting to a (large diameter??) line, passing back through the firewall Along the Left Frame Rail, passing behind the engine to the Right Frame Rail, and running forward to connect to the Compressor Inlet.

Compressor clutch is tied into the dual electric cooling fans such that if the compressor is engaged, the fans are automatically turned on.

WHERE in this system do I need to place the Binary Switch (High pressure cut-out). I'd imagine it would go in the line coming from the condenser to the accumulator, similar to how it is installed on my old ford van.

WHAT parts am I missing?

Are the flare-type fittings available still? The evaporator has brass flare fittings on it, and so does the compressor.

Is it good practice to use hardlines when possible, and hoses when needed? Similar to a hydraulic system?

Once the plumbing is complete, I can charge the system with R134a easily enough. I have a good quality gauge set and a vacuum pump (I build lasers and have a few roughing pumps that would make an A/C service pump look like a kid with a soda straw) and have charged systems with R134a before.

I can provide photos of the car, the above components, and any other parts I can come up with to make this system work reliably and effectively. The mismatched parts don't bother me in the least, as with any custom car it's the price you pay.

The plumbing work doesn't scare me, I can weld and braze just about anything to anything. If I can get copper or brass flare-to-O-ring conversion fittings (I can machine them if someone can get me dimensions) then I'll convert the flare fittings over to O-ring fittings on the evaporator...probably not a good idea to heat the compressor up that much.

Can anyone here offer me any guidance or answers? This is the last major project before i can call my ride finished.

bohica2xo on Wed June 02, 2010 2:21 AM User is offline

Sounds like you have a good start.

1) The HPCO should be close to the compressor discharge - that way a restriction in any component will trip it.

2) Flare fittings are still used. We went to the moon (and back) on 37 degree flare connections - keep using them. The site sponsor can get you virtually any fitting used on a system, and sells a nice line of affordable hose crimping tools as well.

3) Hard lines are great if you can fabricate them. Obviously you need some rubber in the system, but keeping it to a minimum is a smart move.

4) Be careful with that roughing pump. MVAC only needs between 400 and 1000 microns. Below 400 microns, you are asking too much from the shaft seal - it was designed as a pressure seal.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Xnke on Wed June 02, 2010 1:41 PM User is offline

Sounds good. I'll set the roughing pump to 800 microns, (won't pull past the setpoint) and talk to ACkits about changing the fittings on the condenser and getting a drier that will work with flare fittings.

How would I best determine the amount of refrigerant and oil needed? I can get the nameplate data off the compressor for oil requirements, but would I need to know system volume to figure the amount of refrigerant?

Do the hardlines absolutely need to be aluminum? Will copper lines work, similar to a home A/C system? (while aluminum is cheaper, copper is much easier for me to find and simpler to braze)

Xnke on Wed June 02, 2010 5:59 PM User is offline

After spending some time with the tape measure and a lot of headscratching, I will have to find a smaller evaporator core. There just isn't enough room behind the dash to fit it in place.

The ideal core would be around 6" tall, and about 9 or 10" wide, and about 2" thick or so. Is there anything even remotely close to these dimensions available? If not, something about 8"x8" and reasonably close to 2" thick would be workable as well.

The current core is about 4.5" thick and 10" square. I just can't find a configuration that will let it fit properly.

bohica2xo on Wed June 02, 2010 7:51 PM User is offline

Oil capacity is a function of refrigerant / system volume - more or less. Think of the system as a 2 stroke engine. A percentage of the refrigerant in circulation needs to be oil. Some of the original oil charge ends up clinging to internal surfaces. The quantity in circulation is slightly less than the total oil charge.

There are a lot of evaporator cores out there. I seem to recall the 1994 Tempo had a square brick for an evaporator, might have been close to the 8x8. Plate & fin too. The 1988 Audi 5000 had a roughly 2:1 rectangular evaporator, but I can't recall the dimensions... The 1994 Audi S4 also had a rectangular core, but ti was a high capacity serpentine unit.

Lots of choices out there.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

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