OFN Cross contamination

[Argus]

There is an interesting problem that crops up from time to time.

EN 378 is quite specific on the subject of pipe work pressure testing using OFN.

However, there comes a time where pipes have to be pressurised on existing systems where the condensing unit or pack contains refrigerant, or even new systems that come with an operating charge. All that stands between the refrigerant and the high pressure OFN is often a quite basic service valve ? frequently the shut off rate is less than 100% and they let by.

Inevitably if the pipes are coupled when the pressure test and the drop test take place, some of the OFN enters and contaminates the system. This happens more often than people admit to, I think.

If the pipes are tested separately from the unit before coupling to the unit, the final joint to the service valves will not have been tested to the same integrity as the rest of the system.

The real answer, I know, is to remove the entire charge and to pressure test the whole system, but in the real world this isn?t going to happen?..is it?

Interested to hear your views
________
Plymouth Deluxe history

[herefishy]

Hi argus,


Have you tested a system and the refrigerant charge become contaminated?

[Argus]

Not personally - I'm not in that line of work anymore, but it does happen, the practice here is quite widespread, especially with small systems (say up to 20 or 30 kW). My belief is that the refrigerant should be removed.

The relevant European standard is silent on the prospect of the pressure difference across the material of a basic bog standard shut off valve, where, for the duration of the test, the system is inhabited by two substances with the likelihood of cross contamination if the valve seat leaks through ( which many of them do).

I think that this is a short cut to be avoided.

I'm interested in others' response, because there are basically two problems. If and when you do get a mixture, the reclaim systems available and the cylinders supplied for used refrigerant are teted and rated for the saturation pressures for their respective refrigerants - not for the mixture containing a trans-critical substance at a higher pressure.
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Ford XK Falcon

[frank]

Even more critical now that we are using the high pressure refrigerants such as R410a with a reccommended pressure test of 600 psig.

[Andy]

Hi Argus
EN378 talks of strenght testing and pressure testing. Strength testing is 1 to 1.3 times allowable pressure, leak is something like 0.9 to 1.0 times AP.
I would strength test to 1.1 time AP for a brief period i.e just up to test then blow it down to leak test pressure. The leak test can also be brief say 30 minutes. Fitting a gauge on the side not being tested is a good idea, if that pressure rises you then need to take the test back to the next set of shut off valves, recovering the refrigerant in that portion for distruction.
If you do get a little amount of OFN into you fridge system it is easily removed at the condenser by purging, if only OFN is detected, or recovery for distruction if gas/OFN is present.
If you are concerned about A/C splits and such, why not just get them supplied with a holding charge only that is the way to go I would say.
Regards. Andy

[Bones]

Sounds great, but it is hard for manufacturers to make sure every system has a proper holding charge in it... 6 out of the last 10 splits i've installed were actually sealed properly with a holdng charge from factory, the rest has loose flare nuts. LOL thinking of it now i had one split with the liquid line half soldered in, i wonder how that one passed strict pressure testing?!?!

luckily it was found before all was too late and 2kg of 22 was in the blue bottle. i would like to see a backyardy (thats what we call guys who show up and literaly throw a split onto a wall - cause well thats what it looks like for cash on sat & sun) would have done after he purged the system, instead of vac?

maybe he gets the customer to ring us for warranty, thats why we get alot, and the funny thing is they never remember who installed their a/c, not for the life of them! you feel like saying, if you tell me i will be here for 5 minutes, rather then 5 hours depending on who put it in

[Latte]

Theres surely only two ways to avoid cross contamination.
1) Pressure test at LESS than the holding charge pressure.
This obviously would not satisfy EN378 or give the pipework a real test.
2) Reclaim gas and check the whole system.

I must admit, i have never heard of it happening but then again would you admit to it !!!!!!.

Personally i would reclaim/test/recharge. If the job is chargable surely you should quote to do the job right. With R410/R407 i wouldn't like to risk the system by cutting corners.

[Coolie]

When I used to install, I strengthvtested the pipework seperately from the outdoor unit, then released the N2 and tested the final joint up to 100psi.
It was just standard practise for me. If you have good a quality flaring kit then there should no be a problem!

I must admit that I have contaminated the refrigerant on two occasions by the means you describe, thus the new approach!

[Coolie]

That was before R410 came into use, now I'd probably reclaim!

[Gary]

The pressure in a precharged unit will correspond to the surrounding temperature, therefore there should be no possibility of cross contamination when testing the rest of the system at or below that same pressure. Even then, it should be assumed that a valve can withstand some limited excess amount of back pressure. If we don't get carried away, it shouldn't be a problem.

[Coolie]

The pressure in a precharged unit will correspond to the surrounding temperature, therefore there should be no possibility of cross contamination when testing the rest of the system at or below that same pressure. Even then, it should be assumed that a valve can withstand some limited excess amount of back pressure. If we don't get carried away, it shouldn't be a problem.

I was only testing up to 300 psig when the contamination occured.

[Dan]

Inevitably if the pipes are coupled when the pressure test and the drop test take place, some of the OFN enters and contaminates the system. This happens more often than people admit to, I think.

It happens a whole lot in the supermarket trade. As does pulling vacuums on multiple circuited systems, often results in noncondensibles and moisture.

Talking only about existing and operating systems, here, but you must always totally isolate the piping from systems that are connected despite the fact you have isolation valves.

• Never pressure test a multicircuited system with Dry nitrogen unless you cut the pipe loose and loop it.

• Never pull a vacuum on a multi-circuit system, unless you cut the pipe loose and loop it.
  

By looping, I mean soldering the liquid and suction lines together at each end. If you are testing an evaporator or condenser, you solder the inlets and outlets together. Completely isolated from the operating system (or the system soon to be restored to operation.)

I can tell several sad tales where a technician followed "good practices" and caused horrendous results.

One of the aspects of the Montreal protocol that I admire, is that it permits repairs without going below atmospheric pressure under circumstances that may have unknown leaks that could draw in air and moisture.