Metric to SAE/standard A/C plumbing questions

[pete_89t2]

I'm helping a buddy restore the A/C in his old 2nd gen RX7, and since OEM condensers are unobtainable, we sourced a generic parallel flow unit, which has the typical -8 inlet and -6 outlet MIO connections. Ditto for the generic dryer unit that has -6 in/out MIO ports. My only problem is in plumbing the dryer outlet port back to the evaporator core.

The evaporator core connection to the dryer was originally made with 2x sections of 8mm OD aluminum hard line, with M14x1.5 tube nuts at each end. There's an M14x1.5 union (threaded MIO port/tube nut) that joins the 2x 8mm OD hard line sections. We would like to keep a hard line design if possible. I had a couple of ideas on how we might accomplish this, that I'd like the forum's advice on:

1. Ideally I'd like to just buy a 2 foot "U-bend em" -6 aluminum hard line that has the M14x1.5 female tube nut on one end and a standard -6 fitting on the other end (can make male or female O-ring fittings work here as the hose side of the connection from the dryer wasn't built yet). Unfortunately we haven't found such a product anywhere after an exhaustive Google search. Does such a thing exist?

2. Take the existing 8mm line from the evaporator core, cut off the union end of the tube and TIG weld on an aluminum -6 MIO fitting. Problem there is I can't TIG, and finding a local welder to do a small job like this isn't easy.

3. Buy one of those readily available "U bend em" -6 standard AL hard lines. Cut one end off of that, and cut one end off the existing 8mm OD line and use a Swagelok union to connect the two different tube OD sections. I see Swagelok makes such a union, but was unsure if they will work for sealing refrigerants? We're using R134a if that makes a difference. This would make the plumbing a 100% bolt on affair, no welding necessary.

Thoughts?

Thanks in advance!

[JohnHere]

I'm not familiar with the acronym "MIO." What does it mean, "Metric Input Output?"

[pete_89t2]

Sorry, MIO = Male Insert O-ring fitting

[JohnHere]

Seems like the best solution is to use the Swagelok transition fitting to connect the larger and smaller tubes instead of TIG welding or brazing them. Although any time you combine (stainless steel?) ferrule-type fittings with aluminum tubing (electrolysis factor due to dis-similar metals), you'll have the potential for leaks at the ferrules and/or due to corrosion.

What would be at the other end of the tube that connects to the R/D?

[pete_89t2]

Seems like the best solution is to use the Swagelok transition fitting to connect the larger and smaller tubes instead of TIG welding or brazing them. Although any time you combine (stainless steel?) ferrule-type fittings with aluminum tubing (electrolysis factor due to dis-similar metals), you'll have the potential for leaks at the ferrules and/or due to corrosion.

What would be at the other end of the tube that connects to the R/D?

Thanks. The Swagelok straight union fittings available to go from a 8mm OD to a 3/8" (-6) OD tube can be had in 316 stainless steel, or brass versions. I'm pretty sure both are harder metals than the aluminum tubing, so either should work mechanically according to Swagelok's website. Which would be a better choice with regards to mitigating the dissimilar metals/electrolysis concern? Hadn't considered that.

The other end of that tube that connects to the R/D would be a short length of -6 reduced barrier hose, with a straight beadlock fitting (with R134a service port). That fitting could have either a male or female O-ring end, depending on what we end up with on the hard line.

[JohnHere]

The Swagelok straight union fittings available to go from a 8mm OD to a 3/8" (-6) OD tube can be had in 316 stainless steel, or brass versions. I'm pretty sure both are harder metals than the aluminum tubing, so either should work mechanically according to Swagelok's website. Which would be a better choice with regards to mitigating the dissimilar metals/electrolysis concern?

I'm not a metallurgist, but I would think that the 316 SS, being harder than brass, would be the better choice.

The other end of that tube that connects to the R/D would be a short length of -6 reduced barrier hose, with a straight beadlock fitting (with R134a service port). That fitting could have either a male or female O-ring end, depending on what we end up with on the hard line.

It has been mentioned on here before, but Cold Hose in Florida can custom-make whatever metal lines or hoses you'll need. Might be better than trying to put something together yourselves.

[pete_89t2]

Thanks for the Cold Hose tip - I was aware they do custom hoses, but didn't know they do custom hard lines. Called them and they are going to get beck with me on my request at making up a 2 foot "U-bend em" line with the M14x1.5 fitting on one end and standard -6 on the other. That would be the easy solution for sure!

[JohnHere]

Great...I'm sure CH wll do an exemplary job for y'all!

[Cusser]

I worked in an industrial chemistry laboratory for over 4 decades. SwageLok fittings are absolutely the best, and the by-far most-common fittings used in gas (and liquid) chromatography.

What that means for us here is that these fittings were leak free for hydrogen (explosive) and for helium molecules, which are way smaller in size than refrigerant molecules. And SwageLok fittings are available in different metals to match the composition of your tubing.

So properly installed SwageLok fittings will be leak free and withstand high pressures.

[JohnHere]

I worked in an industrial chemistry laboratory for over 4 decades. SwageLok fittings are absolutely the best, and the by-far most-common fittings used in gas (and liquid) chromatography.
What that means for us here is that these fittings were leak free for hydrogen (explosive) and for helium molecules, which are way smaller in size than refrigerant molecules. And SwageLok fittings are available in different metals to match the composition of your tubing.
So properly installed SwageLok fittings will be leak free and withstand high pressures.

Cusser: Thanks for that bit of information. It appears that Swagelok fittings are something to be considered when repairing or building-up MVAC systems. Very high-quality products usually come with a high price, though.