rejuvenating an old system

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scottjeffrey
Posts: 3
Joined: Mon Jan 28, 2019 5:04 pm

rejuvenating an old system

Postby scottjeffrey » Mon Jan 28, 2019 5:06 pm

Hi and thanks for having me. I am renovating an A/C system in an old 1974 vehicle. I have updated the compressor and condenser, am making new hoses and using aluminum headlock fittings. All fittings will use o rings except my connections at the ancient but excellent condition evaporator. Those two to the compressor and from the dryer will be flare fittings. I am wondering if I should use copper flared washers and whether or not the dissimilar metals is going to be a problem. The fittings from the hoses will be aluminum, the expansion valve seems like a different metal as does the evaporator side fitting to the compressor hose. I am planning on using Nylog Blue after reading about it in my searches and am trying to get this right the first time. I will be using R134a refrigerant.

Thank you very much for your help. -Scott.
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bohica2xo
Posts: 580
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: rejuvenating an old system

Postby bohica2xo » Mon Jan 28, 2019 5:16 pm

Flare fittings will be just fine. You should not need a copper washer - unless you have a damaged fitting.

Use an anti-seize compound on the threads. Clean & dry on the mating surfaces is just fine.

On flare fittings without a sleeve I like to use a little EP grease or anti-seize on the backside of the flare where the nut contacts the tube. This keeps the nut from twisting the tube as you tighten it.

Torque them up & go to lunch. Re-check them for torque before putting them in service.
scottjeffrey
Posts: 3
Joined: Mon Jan 28, 2019 5:04 pm

Re: rejuvenating an old system

Postby scottjeffrey » Mon Jan 28, 2019 5:32 pm

Thanks so much! Anti-seize on the threads and is Nylog Blue good for the flare contact surface itself? I hear you need to tighten them up, extra tight, correct? Thanks so much bohica2xo!
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bohica2xo
Posts: 580
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: rejuvenating an old system

Postby bohica2xo » Mon Jan 28, 2019 6:46 pm

I prefer to keep the sealing surfaces clean & dry. If you get something slippery on that mating surface the tube wants to twist with the nut.

The original flare fitting is designed for metal-to-metal contact. It is a dependable system that seals nearly every propane & natural gas appliance in North America.

To tighten flared tube fittings, especially used parts & mixed materials you should use an angular displacement. The JIC term for this is FFWR. Here is how it goes:

Assemble the fitting, and with the correct wrench on the hex nut tighten the nut until resistance is felt. I recommend 2 fingers on a standard wrench. You can feel the torque come up as the mating surfaces touch. Stop there.

Use a permanent marker to draw a line down the length of the tube / nut / fitting. Use the center of a wrench flat on the nut if at all possible.

Tighten the nut ONE more wrench flat (60 degrees) so that the line on the tube & fitting line up with the center of the next flat on the nut.

The displaced line on the nut also serves as visible proof that you tightened the nut.

Since most people do not have wrenches to torque to a value on a tube, the industry has relied on rotation for decades. For reference the torque value for a -8 tube is 47 ft/lbs.
scottjeffrey
Posts: 3
Joined: Mon Jan 28, 2019 5:04 pm

Re: rejuvenating an old system

Postby scottjeffrey » Mon Jan 28, 2019 6:53 pm

Very interesting and very helpful. Much appreciated! Come over this weekend, lol.

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