Pressure Testing with Nitrogen

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Pressure Testing with Nitrogen

Post by DHallworth »

Evening Gents,

This isn't a problem I have with one of my French cars, it's my old P38 Range Rover but there's a huge number of knowledgable people on here so I thought I'd ask :)

Last year I fitted a new condenser and drier and had the air conditioning recharged. It held a perfect vacuum test when it was on the machine and the engineer even commented that it was unusual for a car of that age to hold such a good result on the vacuum test.

Unfortunately, my joy was short lived as when I got home I was checking something under the bonnet and I could hear a hissing noise. One of the aluminium pipes that run along the bulkhead has a pinhole in it and it was leaking refrigerant. I've replaced all 4 of the aluminium pipes under the bonnet but am worried about getting it recharged again.

The cost of recharging it has increased significantly recently due to a huge increase in the cost of the gas and as the Range Rover holds 1.5kg of gas the cost of a recharge isn't insignificant these days as well as the environmental impact of leaking the gas straight back out!

This got me thinking... I have a huge nitrogen cylinder in the back of the workshop that I use for recharging the Citroen spheres. I was wondering about filling the system using a charging rig that's available online to connect the Nitrogen cylinder to the filling ports. At least that way I can leave the pressure gauge on it for a week to check for any leaks before having it recharged.

If I can get a set of gauges, does anybody know what pressure to fill the system to? I don't want to dump to much in and find it blows a hole in the new condenser.

Any thoughts/suggestions would be much appreciated.


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Re: Pressure Testing with Nitrogen

Post by wheeler »

A/C systems should be checked using nitrogen, a vacuum check is not really a good way to check a normally pressurised system for leaks. If you vacuum a circuit that is normally under pressure you can actually seal a leak. The reason for vacuuming the A/C circuit is to boil off any moisture in the system, it only really serves as a very basic leak check.
Anyone doing A/C refilling now is meant to do a pressurised leak test before filling the system as I believe is now illegal to knowingly refill a system that is known to be leaking.
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Re: Pressure Testing with Nitrogen

Post by quintet »

I've done pressure testing on countless cars using nitrogen in a previous job and im pretty sure we used to take them upto about 8bar. We used BOC for our gas supply but i'm not sure what size the nitrogen bottle was but it pretty much maxed out at that point.
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Re: Pressure Testing with Nitrogen

Post by white exec »

I'm interested in doing that kind of pressure test too, David, as I need to do a conversion from R12 to R134a on the BX, and would like to check for any leaks, not least on the replacement O-rings I'll need to fit.
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Re: Pressure Testing with Nitrogen

Post by Hell Razor5543 »

Although he has not been on the Forum for a while you might want to give DickieG a shout. He has the proper a/c equipment AND the knowledge about what amounts should be used (either that or where to find that information).