Just wondering how long do you leave the pump on the condencer? For 1.5 and 2 T I usually leave the pump on for about 20 to 30 min. Yesterday and today I installed 3 - 5 tonns and 3-4 tonnes at a new building . Tomorrow I'll vac them out for about 30 min each. If you don't mind me asking, what's your prefrence and why?

Though I usually work on window units which are 1 ton or less, I run the vacuum pump A few minutes after I get to 28, then I shut it off. Then I do something else for 10 minutes. If I have a leak it shows up on the gauge.

I work on central systems and I do the same as shunned, I pump it down to 28 or so and then I do one thing more, just to make sure that I have all the moisture out I heat the exposed lines just a few degrees and then wait about thirty minutes to charge the lines. If it is a compressor change out I heat the condenser coils a bit also.

Use a micron gage it will not lie. If you have moister in the system your freon gage will not pick it up. Change the oil on our vacum pump.

I agree with t-top a micron meter will save you a world of grief it is far more sensitive than standard guages. My first pump I rarely changed the oil, and I wore it out in a couple of years.

Please change the oil often. For more reasons than just longer pump life. If you vac a burn out unit, or a unit that was high in moisture, the oil suffers. Mineral oil is hydroscopic, this means it can absorb water, ester oil POE's are even worse. The pump vacuums the condenser through it's own oil, that moisture boils out of you pump oil, making your pump down times longer and harder to obtain 500 microns.