Automotive Air Conditioning Information Forum

Newbie question, I have a second hand Yellow Jacket vacuum pump which seems to work well, I drained and refilled the oil but when I used it there was vapour coming from the breather on the top.
Is this normal, is there a problem with the pump or is it showing there was a lot of water in the system being vacuumed.

The car was my own classic which had an R134a conversion 8 years ago and as the a/c was gradually getting worse I decided to fit a new dryer and refill with the correct weight of gas. The system is now operating great but I just wanted to know what the vapour was.

Jaz wrote: ↑Thu Feb 24, 2022 1:45 am I drained and refilled the oil but when I used it there was vapour coming from the breather on the top.

My guess is that the visible vapor was some mist from the vacuum pump oil.

My primary vacuum pump was given to me when the R&D of our sister company was moving to another state. I was told that the vacuum pump smoked, and I told them I wouldn't be using it inside. Anyway, hasn't smoked when I use it, and I've been happy with it even though it is somewhat heavy to carry.

Overfilled?
There is a sight glass with a mark.
Correct type of oil?
Vacuum pump oil is especially for vacuum pumps only

Google search your exact make/model and see what you come up with

Its a Yellow Jacket pump and I bought Yellow Jacket oil and drained the pump and filled to the line on the sight glass.

Then I would not worry about it.