Quote Originally Posted by monkey spanners View Post
I think they used to break the vacuum with refrigerant. That way if the pump only gets out 98% on each vac by the third one there is very little air left in. I think the moisture thing is a bit of a red herring.

People also tend to think if one of something is good then more must be better.

There may be a case of people not wanting to appear lax in their working practices so they claim to do what they think or have heard is best practice. I for example never ever braze without ofn...


I have found on systems that are taking a long time to vacuuming that putting a few bar of ofn in and starting again helps speed things along, i suspect the slowness is due to refrigerant disolved in the oil and the ofn going in stirs the oil up a bit (often movement can be seen in the comp sight glass for example)

Jon
Indeed - the idea was that the first vac would leave 4% contaminants. Then the next 4% of 4% which is 0.16% and then the next was 4% of 0.16% which gives basically 0%.

But I'm not sure whether it would mean the next vacuum was quicker after stopping to introduce a little nitrogen. Did you ever stop to introduce a little air and see if it was also quicker second time