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Pulling down AC

D

David G

Well-known Member
Do you think it will hurt anything to leave vacuum pump on for two hours on AC?

I want it to suck down good, and cold going out to shop.
 
We would leave the vacuum on for hours on a system that had been open to remove moisture. Shouldn't hurt a thing.
 
Thanks

I do plan to close the valves and let it sit overnight with vacuum and see if it holds.
 
Longer the better although not usually necessary. I usually leave vacuum pump on for 2-3 hours and see if it holds overnight unless I am in a hurry to finish the project. When working for a dealer in the field, 1/2 hour and charge then leak check.
 
The danger of pulling a vacuum too long is you can boil the refrigerant oil. You have to get below 250 microns to do that; a good vacuum pump can pull 50 microns or less, but that's not the whole picture. Most hose sets aren't good enough to pull a decent vacuum, even if your pump is up to the task. If you use copper line instead of hoses, you'll have better results.

Bottom line: you'll never know what's actually going on without a micron gauge. You can buy a decent gauge for 150 bucks. Without a micron gauge, I wouldn't worry about two hours using a typical pump. If this is a new unit where the refrigerant is still sealed in the compressor, there's no risk of boiling the oil since it's segregated from the vacuum until you open the valves.
 
David D,

No,,,,it will not. Even if it holds vacuum overnight, it will show some loss on the gauge. A little loss though is normal,.
But a few inches is an indication of a possible leak.

Guido.
 
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