Domestic Refrigeration R600a Question

Hi guys, just joined the forum all though have been reading it for a few months,i have a question or two on repairs to domestic R600a units.

just some background I'm an independent engineer that does some contract work to the large Italian Manufacture, been doing the electrical for years but iv been doing refrigeration for about 2 years with them and there is an few issues that are bugging me

We seem to see a lot of R600a units with no or low gas symptoms, we vent then evacuate and hold for 1 minute to check for leaks, they always generally pass the hold on this test, short of acut pipe they normally do hold vac, on the system pipework there is a anti condensation fed that runs around the front where the doors are to prevent sweating, this is fed directly from the high side before the condenser.

Recently we have been told that if we have a unit where there is no signs of leaks on the vac hold test we should cut and bypass the anti condensation circuit, this is due to that pipework being steel and are known to rust through on the lower corners, annoyingly will always pass a vac test though, its a simple 5 minute job as the feed and return are all next to each other.

now i'm not a fan of this as its 90% the customer will be calling back complaining after a month when they see water around the door however my main concern is charge weight, obviously R600 has very low charge levels, most domestics are around 40g, i was also taught that r600 has a charge accuracy of 1g so it must be correct,

The question no one can seem to answer is should we not be reducing the charge when bypassing this anti condensation curcuit ? it a large length of pipe work, its got to be equal to the condenser in length.

its bad enough with these systems that you go in, diagnose no or little gas, do a full test system and not really find an issue, do a full system repair and walk away with fingers crossed it wont recall a week later.

Sorry for the long post but wanted to try and explain fully and its really bugging me now

thanks in advance

For a start a one minute vacuum test is not a legitamate leak test. All you are doing is pressurising the system to effectively 1 bar, 14.7 psi,with external air pressure.

As regards the change of system volume by cutting out a section of high pressure gas line you could calculate the volume reduction by measuring the pipe length etc or you could ask the manufacturers as are are the "design team".

Silly question but just trying to cover the basics. Are you changing the drier before degassing. Certain units do have a nasty habit of choking driers if they overheat which will give low gas symptoms

Obviously, that should have said "regassing" not degassing

I was trained by the manufacture them selves on there own in house training centre, they state a 1 minute vac hold test to check for leaks, iv never believed a minute is long enough but that there policy, as for shorting system length and reducing the charge I have asked multiple times however no one has an answer.

Also Yes the drier is changed on every system thats broken into,standard policy,

I wanted to get an idea of you guys thoughts on it

I would go with blocked drier being the problem, how long does the factory evacuate these for before charging? Definitely 1 minute vac test no use, pressurise system (before drier change) with nitro to high pressure then hold for an hour or more.
Anti sweat pipe should take years to rust out (unless very poor quality pipe). If removing it, recharge with original charge then check for increased discharge pressure or raised current draw, this will indicate is system is then overcharged and needs to be reduced.

If you do pressure test with OFN make sure the evaporator will take the higher pressure. Some domestic style fridges have a plate evaporator which can bulge out permanently if subject to test pressure designed for the high pressure side.

Cheers,
Andy.