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Nitrogen Pressure Testing Procedure

seagull369 on Wed July 16, 2014 11:51 PM User is offline

I wanted to test my car's r-134a system for a leak using compressed nitrogen. I have all the equipment I think I'll need (bottle, regulator, fittings, ac manifold) to do this, though I'm just a little unsure how to proceed with it. Would I be able to pressurize the low side in one test, then the high side in a separate test (checking for leaks each time) or should I pressurize the system from the low side only?

I've read somewhere when doing this test the low and high sides should be pressurized simultaneously each with their respective pressure values (lower pressure on low side and higher on high side), but I don't think I could create two seperate pressures in the system at once with the gear I have...

Any thoughts?

Edited: Wed July 16, 2014 at 11:56 PM by seagull369

alan73 on Thu July 17, 2014 6:40 AM User is offline

the leak testing is done with the system not running so would expect the pressures should equalize regardless of witch side you add to but you can probably confirm this with your gauges and add to both sides if needed and you will be just using the 1 pressure to test both sides, while I have never used nitrogen for leak testing I see 175 -200 psi recommended.

wptski on Thu July 17, 2014 7:51 AM User is offline

The gods here say not to go over 150psi. The pressure should equalize on both sides if only applied to one side, if not, you have a blockage.

seagull369 on Thu July 17, 2014 9:46 AM User is offline

Thanks for the great info. I didn't know about the pressure equalization thing. I'll report back to let you know how it goes..

Dougflas on Thu July 17, 2014 10:09 AM User is offline

If you have a sniffer, first put an oz or two of refrigerant in the system and then use the N2. The sniffer should pick up the leak area.

HECAT on Thu July 17, 2014 10:27 AM User is offline

Pressure equalization is what happens to the operating high and low side pressures (they equalize) when the system is shut off. There is no more suction or pressure being created by the compressor, and the orifice (OT or TXV) allows the high pressure to continue to bleed toward the low side until pressure equalizes (some equalization can also back bleed thru the compressor itself).

You have to first recover the refrigerant and do not attempt to run the compressor. You can then charge nitrogen into either the high side or low side regulated at 100 to 200 PSI (150 would be my preference). I have heard of 250 PSI damaging low side components (evaporator) but maybe it was already on its way out. If your high and low side gauges to not read equal pressure after just a moment; this could be an indication of a solid/hard restriction somewhere in the system. Once charged, you can listen or soap test for leaks. Adding a small amount of refrigerant and using a electronic leak detector can also be done.


HECAT: You support the Forum when you consider for your a/c parts.


TRB on Thu July 17, 2014 4:21 PM User is offlineView users profile

Big Blu works great for finding leaks when system is under pressure.


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

seagull369 on Fri August 15, 2014 12:04 AM User is offline

seagull369 on Fri August 15, 2014 12:33 AM User is offline

I found the leak in a hose leading to (or away from) the compressor. Only had to pressurize to about 70psi before it started hissing. Hose was replaced, system was pressured again to about 100psi (I was chicken to go any higher). Let it sit for a half hour and it held on both sides. Vacuumed for a half hour then let it sit for another half, and it held (not sure if it was necessary to do that latter step since it didn't leak under pressure, but figured it wouldn't hurt). Recharged system and it's working fine now.

I fibbed earlier about using nitrogen. Don't actually own a tank of that (yet, anyways). I used argon from my TIG setup instead. I noticed a thread on the site here which said argon was OK to use, so figured I'd be safe.

Many thanks for all the help.

Edited: Fri August 15, 2014 at 12:40 AM by seagull369

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