Pressure Testing with Nitrogen

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DHallworth
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Joined: 20 Nov 2005, 18:05
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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.

Thanks,

David.

wheeler
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Joined: 21 Sep 2002, 19:07
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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.