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Originally Posted by Shophound

I think what the OP may mean is that he used wet rags, brazed the leak, THEN pulled a vac and opened the valves only to find a problem.

Yeah, you're right... that has to have been what he meant. I saw the "but system under vacuum" and didn't mentally change it to "put system under vacuum". When I do that, it's obvious--as it was already obvious to you more experienced folks. Thanks.

I was wondering why someone would have a vacuum pump running while brazing, and the answer is that they wouldn't.

Keith

Originally Posted by Bladeforger

As said, you need to know subcool, superheat, AND those pressures.

However, I'd not braze a lineset with a vacuum on it because the vacuum would be trying to suck some braze into the lineset. And carbon. Bad juju.

Keith

I don't see how you could hold a vacuum on a piping joint that is unbrazed. The joint would leak too much.

I think what the OP may mean is that he used wet rags, brazed the leak, THEN pulled a vac and opened the valves only to find a problem.

OP, hindsight being 20/20, it's better to recover the entire charge and flow nitro like has been suggested. Now you may have trash in the system due to internal carbon buildup while brazing that busted loose and is now in the metering device. Also, a liquid line drier should have gone onto the liquid line. Which means at times you must remove the one inside the condensing unit if there's one already installed there. So it's better to recover the entire charge, flow nitro, and braze up everything at the same time.

Why a vacuum

Originally Posted by Ron223

I would have to agree with Cobitech, you need to know all of your parameters. With out them you don't really know and depending on the load that may not be any problem. Also, I don't know that its a good idea to braze while the lines still under a vacuum. Just a side note.

Why not use nitrogen to pruge with around #1 to#3 lb.

Depending on where you are they may not be out of line. Suction to me is a little low but it's 100° plus here. More info is needed.

As said, you need to know subcool, superheat, AND those pressures.

However, I'd not braze a lineset with a vacuum on it because the vacuum would be trying to suck some braze into the lineset. And carbon. Bad juju.

Keith

I would have to agree with Cobitech, you need to know all of your parameters. With out them you don't really know and depending on the load that may not be any problem. Also, I don't know that its a good idea to braze while the lines still under a vacuum. Just a side note.

Why do you think these pressures are out of the ordinary? What is the superheat and subcooling? what is the inside and outside temperatures?

Sounds like an issue that needs an experienced tech to look at in the flesh.

A simple braze job, now a slight problem.

Just had a unit that a month and a half ago was low on charge. I charged it and with in 3 week it froze up again. Found leak but did not have tools to repair. Went back to make repairs on discharge side and to save time I shut the valves off at condenser and recovered gas. I normally just leave them alone but didn't this time. Placed a wet rag of valve and made the repair, but system under vacuum and opened valves. Now pressures are not normal. High suction and low head (64 suction, 165 head, R22). My question is could I have done something to the discharge valve while soldiering to make these pressures like this? I have worked on units like this at work and on the side and have never had this to happen. I'm just beside myself on this one.