Unable to locate leak

[kay86]

Hello! I've just completed the brazing process, tried to test with 12 bar argon and I notice that the pressure drops by 0.02 bar every hour. I used hvac foam to test the joints but I wasnt able to detect anything. At this point I am not sure the leak is in some joint or on the gauge. I am using blutooth Testo gauge without hoses so it shouldn't leak by any tangible amount.
Also, I wasnt able to pull a good vacuum, as I reached 700 micron but was back to 2000 micron in 30 minutes or so.
Any suggestion would be much appreciated!
Andrea
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[seanf]

I would have two gauges on the system, one on the low side and one on the high side to make sure the pressure is equalised completely.

Then start with a leak test at a lower pressure, maybe 2 bar, and then check everything for bubbles including your gauge connections, and any schrader valves.

Then bring the pressure up, maybe to 6 bar, and re-check for bubbles.

As well as your hvac foam, you could also try slightly diluted washing up liquid, or even some light oil to check.

If nothing shows up,

Put it back up to 12 bar. Leave the system to sit for awhile to equilise the pressure, and with the temperature of the room.
Record the pressures on the gauges, and record the temperature of the pipework and the room temperature.
Leave the system for say, 12-24 hours.
Then record the new pressures and temperatures.

Then using absolute pressure and absolute temperature values,

Use P1/T1 = P2/T2 to see if the pressure drop is from a change in temperature, or from a leak.

Other places you sometimes find leaks are,

Around the pins of the electrical connection of the compressor.

Pin holes in copper tubing / copper spun filters / copper spun accumulators.

Small leaks in brazed joints, sometimes the residual flux from silver solder joints helps to hide them.

The welded seam of the compressor. And the joints of the tube stubs to the body of the compressor.

And if you have access to an electronic refrigerant leak detector, you can add some refrigerant to the system, and then pressurise it higher with your argon, then use the electronic detector to sniff around the system.

Hopefully others will see your post and give better advice.

[kay86]

Hi Sean, thanks for your advices. Do you have an opinion on ultrasonic leak detectors? I'd consider buying one but I'm afraid there's a limit on the size of the leak that you can observe with such instruments. I've watched some YT videos and they also did a bubble test and the leaks where bubbling vigorously.

[seanf]

I've never used the ultrasonic type detectors before, sorry. If you do buy a detector, make sure it can detect the refrigerant your using.

Sometimes you get lucky and the leaks give obvious bubbling.
Sometimes though the bubbles can be so small you really have to sit and watch for a little while, the bubbles can look more like white foam.
Sometimes instead of bubbling, when the soap goes over the leak the pressure just sprays the soap off the pipe.

[paulc1978]

Overnight pressure test to approx 1.3 x high side operating pressure, allow 0.2 bar drop for ambient temp reduction, if system has shell and tube evaporator be sure to segragate this and pressure test to 80% of its max test pressure.