Vacuum.

[Drew]

I've been pulling a vacuum on a big VRV system which has been retrofitted . We reclaimed all the old R410 and fitted new indoor and outdoor units using existing pipe work. All Bs boxes and indoor units have flare fittings. I have been trying to pull a vacuum and am not sure if I've got a leak because I can't get it down past 20000micron. I've had the pump on for 8 hours. Because of all the oil polyester oil in the pipes could I be battling to get the vacuum? Or do I have a leak. It held 400 pasig for 12 hours.( nitrogen).

[Glenn Moore]

Hi Drew
Could be a few things.
1) POE is highly hydroscopic (absorbs water) so how long was the system open to atmosphere as moisture ingress can be very quick, with POE.
2) IS the vac pump big enough
3) Have you changed the vac pump oil ?.
4) The pressure test sounds good, so try breaking the vacuum with nitrogen, and re vacing the system to see if any improvement.
5) Energise the compressor heaters and any other heaters on the system to help remove any moisture during the vac
6) Try another vac guage to double check

If no improvement its back to re gas testing
Best of luck

[CONROD]

Have you removed the shraeder valve cores from the service valves as this makes a big difference - recently on a new install left a vac pump on all weekend, couldn't pull a decent vac, so removed the shraeders, 12 house later bingo, 0.5 torr...

[moideen]

Hi Drew
Could be a few things.
1) POE is highly hydroscopic (absorbs water) so how long was the system open to atmosphere as moisture ingress can be very quick, with POE.
2) IS the vac pump big enough
3) Have you changed the vac pump oil ?.
4) The pressure test sounds good, so try breaking the vacuum with nitrogen, and re vacing the system to see if any improvement.
5) Energise the compressor heaters and any other heaters on the system to help remove any moisture during the vac
6) Try another vac guage to double check

If no improvement its back to re gas testing
Best of luck

glenn, you are correct, i have same experience before,after replacing vac pump oil reached to 500 micron.

[Grizzly]

Have you removed the shraeder valve cores from the service valves as this makes a big difference - recently on a new install left a vac pump on all weekend, couldn't pull a decent vac, so removed the shraeders, 12 house later bingo, 0.5 torr...

Basic advice, but highly relevant all the same.
But Not for Drew methinks!
Sadly some joints can be gas tight at Positive Pressure, but leak under negative pressure.
An interesting post Drew.
Thanks Grizzly


Grizzly

[monkey spanners]

Try a vacuum rise test, maybe isolate outdoor units and just vac pipework and indoors, used compressor oil can be a pain to vac due to the refrigerant dissolved in it but 20,000 sounds a high vacuum to get stuck on.

Is the vac gauge accurate?

[Drew]

Thanks for the replies guys.
We re pressurised the system and found a leaky flare. Confusion with regard why it held pressure previously? Their has been talk about us not have driven all the bs boxes open correctly. I am easily confused when I have to push certain buttons in sequence and might have only pushed the set button 20 times instead of 21? It held pressure and pulled a decent vacuum after repairing the flare.
these VRV systems will be the end of me. I feel sorry for the apprentices coming through having to face these. I hardly recognise anything in the outdoor units anymore.
thanks again.

[chemi-cool]

Add on of these to your tool box and kiss leaky flare nuts goodbye.

http://refrigtech.com/Product/Sealan...ylog_blue.html