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Sealing barrier hose with clamps

mmartin454 on Mon March 13, 2006 12:18 AM User is offline

Year: 1969
Make: Pontiac
Model: GTO
Engine Size: 400
Refrigerant Type: 134
Country of Origin: United States

I am replacing the A/C hoses on my 69 GTO and would like to retain the original look by reusing the screw type clamps that the car was built with. I would like to use barrier hose but understand it is difficult to get a good seal with the screw clamps. Does any one know of a way to get a better seal and still use the original clamps ? Can a sealer (such as silicon, permatex, etc.) be used on the barbs and inside the hose to help get a better seal with the nylon inside the barrier hose ?

TRB on Mon March 13, 2006 10:08 AM User is offlineView users profile

OEM never used hose clamps on their connections that I know of, even back then. I would not use a hose clamp with barrier hose you are just looking for problems when doing so in my opinion.


When considering your next auto A/C purchase, please consider the site that supports you:

clueless on Mon March 13, 2006 11:01 AM User is offline


60's GM cars had hose clamps with a bracket that went over a flange on the fitting they are likely original clamps on a 69.

Not sure when they went to swaged hoses but a 70 Elcamino I worked on had swaged and a 68 had the hose clamps.

WIll find a picture of one.

mhamilton on Mon March 13, 2006 12:56 PM User is offlineView users profile

In the early '60s GM offered a 2nd a/c system that I guess was cheaper than the full factory system (I think it was dealer installed), only used recirculated air and had screw clamps.

clueless on Mon March 13, 2006 5:22 PM User is offline

These are off of an 68 Impala with factory installed manual controlled A/C.

mmartin454 on Mon March 13, 2006 10:26 PM User is offline

Yes ? Those clamps look just like mine. Any ideas for methods of getting a good seal using these types of clamps ?

bohica2xo on Wed March 15, 2006 4:21 AM User is offline

Ok, I have touched on this before - but I will cover it all this time.

Sometimes it is necessary to use a clamp, or an old fitting, or both. Working on a 100 point car, you sometimes do not have an option... So this is how it can be done.

Barrier hose has a nylon liner to help contain the refrigerant. Nylon does not have as much compliance as earlier rubber hose, and will not tolerate deep scratches in the sealing surface. Sharp corners on older barbed fittings can cut the nylon liner as well. If you must re-use an OEM worm drive clamp you can, but you will need to prepare the fitting.

Here are some example fittings, the top one is an OEM fitting with the hose & crimp sleeve removed. The one in the center has been modified for barrier hose. The bottom one is the worst example I could find.

The top fitting in the photo above would leak with barrier hose and a clamp. All of the small defects, burrs and scratches would provide a pathway for refrigerant leaks. It would be impossible to squeeze the nylon into contact with 100% of the surface of the fitting in the pic below. The linear gouges from the forming operation are typical of a fitting like this:

The modified fitting has been polished to remove ALL of the linear marks from the tops of the barbs, making them into small beads. The sharp edge has been removed to avoid cutting the liner. You can polish a fitting with fine sandpaper, then buff it. Smooth is more important than anything else. The close-up will show you how good the surface should be. The nylon line can easily be forced into 100% contact with the small radius of the beads:

The last fitting would be a disaster with barrier hose. The deep barbs and sharp corners would cut the liner as soon as the clamp was tightened. The handling dings & chatter marks would leak as well:

Once you have prepared the fitting, you need to be sure the hose is warm when you assemble it. Nylon is far more compliant at 150f, than it is at 50f. Warm the hose before you push it together.

The locating leg on the clamp should place the clamp directly over the barbs. Check the clamp on the fitting before you push the hose on - if you need a small gap at the end of the hose for proper clamp location, measure this gap & duplicate it when you push the hose on.

Snug the clamp up, then warm the fitting with a hair dryer or heat gun. 150f is good, do not overheat. While the hose & fitting are still hot, tighten the clamp.

Sometimes it is not a show car issue, but a system that does not have removable fittings (like a corvair evaporator). Replacing old hose with barrier hose means using a clamp. The already mentioned fitting prep is just as important, but I prefer a clamp like the one below, since it does not damage the hose cover, and has more clamping force:

Hope this helps.



"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.

mmartin454 on Wed March 15, 2006 11:42 PM User is offline

Thank you very much ! This is exactly the kind of advice I was looking for. It makes perfect sense now that you have explained how the surfaces need to be smoothed to match with and protect the nylon inner liner. Appreciate the pictures also. Thanks 'B' !

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