I have a small wine fridge with a leak.

Background :
10 years ago my parents bought a cheap Chinese wine fridge. 6 years ago they asked me to look at it because it wasn't cooling. The discharge from the compressor gets routed through an Aluminium pipe that sits below the surface of the door gasket to prevent condensation. The insulation foam contains acid that eventually eats through the Aluminium tube, so I bypassed the tube and lopped about an inch and a half off the cap tube as it was plugged solid. Put a new oversized dryer on it and did a few nitrogen purge/vac cycles. Left it under vacuum for a day or so and it held at under 100 microns overnight, so I put 50g of r134a in it and called it good.

Fast forward 3 years and it's stretching its cycles out and not cooling as well, so I weighed the gas out to the best of my ability and it was well short. Vacced and put 50g of r134a in it as it was the start of the holiday season and they just needed it cold. Give it another 12 months and it is starting to go again, so they replace it and give it to me.

So, the thing holds 50g of r134a and I can charge it within a couple of grams using the gear I have. It appears to be losing 15-20g a year. My leak detector is pretty average with r134a but sensational with r22. To find the original leak I vacced it out (as well as I could given the magnitude of the leak) and put 10psi of r22 in it (static pressure). Backed that up with about 80psi of N2 and the leak detector went nuts as the r22 permeated the foam.

That was a big leak by comparison to what I have now.

So, I've found plenty of leaks before, but none this slow on a system this small. My thought was to do the R22 thing again (I think I calculated that works about at 2 or 3g of r22 in the approximate system volume), but wrap each assembly in cling film and leave it for a day, then poke the leak detector into the film to see if there is a residual buildup of gas.

I also though about 100psi of N2 and some big-blu, but I've struggled with that lately on really small leaks and there is a lot of pipework to check.

This is not critical, it's my own gear and I have plenty of time. I'm also willing to call it quits and recycle it should there be a leak in the aluminium evaporator or pipework. It's more an exercise in learning and if I happen to get a nice glass doored wine fridge out of it that is a bonus.

I brazed up a little transfer vessel to sit on my accurate scales so I can get the charge weight about right, but weighing out a charge that small with a standard recovery machine is a challenge. I do it by vacuuming out the transfer vessel and pipework, then packing the transfer vessel in ice and salt and using the temperature differential to suck out the gas. I can then weigh the end result and its within a couple of grams. If I were really serious I'd use dry ice, but I've only used that when pulling r22 out of burnouts without contaminating the recovery machine.

So, I'm after any old tradie tricks or other advice that might help cut down the hours I'm likely to put into this things.