I have one rep telling me to pull to 250 microns, and another telling me to pull to 50. This is a huge difference as far a time is concerned with our current vac pump. What would you say was sufficient for a vacuum. I realize 50 would be optimal, but 250 sounds reasonable, and would wear less on the pump. Not to mention time spent when 50 or so miles from town with no other jobs near by. Seems a waste to sit on my thumbs, or add extra mileage for two round trips just to pull uneeded microns. But if that is what it takes, I'm okay with it. Just want some opinions.

250 isn't resonable. You have to be below 100 because when your below 100, most of the water is out of the system. You'll probably notice that it stays at 100 for quite some time. The vapor pressure of water is 17.5 um.

Keep the lines capped before install. For tubing cap both ends when in storage.

To help get the water out purge the lines with dry nitorgen and use a heat gun to warm the lines when vacuuming.

So, use prevention first.

Use pump purge cycles second. Purge Nitrogen, pump, purge, pump. You;ll notice that each time it will pump down faster.

Use a heat gun to warm the lines.

Thanks Kiss. So below 100 is fine. 250 is no good. Sounds fair. We do always keep out line sets sealed until install, but since they are only residential units we install, it would be hard to use a heat gun to heat the suction line, unless we stripped all inso. So ill just run the pump longer, get a good pull, or possibly upgrade to a larger pump. Appreciate the thoughts.

Ps. And I agree about the nitrogen purge. Do it on every system. Which brings me to another question. I always pressure up the system with dry nitrogen to 300 psi to check for leaks on my brazing(no bodys perfect) Does this seem a suitable charge for leak test? I then purge the system and put on the vac. I also pull schrader valves during braze, purge, and vac(yes I have the correct epuiptment to reinstall schraders without losing vac). It seems a larger pump would be the ticket here.. Any recommendations on pumps.

Know how to use the ballast on the vaccuum pump if so equipped to remove the water from the pump oil. Oil contamination also plays havoc on pumping. The oil can be outgassing with contaminants.

Purging is MUCH different than say three pump/purge cycles.

Let's pick a number. Say it takes 5 minutes to get to 400 um. Initially pump to 400 um. Add Nitogen. Vent it. Pump to 400 um. Add nitogen. Vent it. Pump to 400 um. Vent it. Do final pump.

You'll find that the system will pump down faster in the long run.

300 PSI should be fine for a leak test, although you would probably do much better using leak-up rate because you have fineer graduations on the vacuum side of the scale, Problem is - both methods take time. Leak-up rate should be an easier test.

Change oil after every use. Oil is cheap insurance.