HVAC - pulling vac too fast and pump selection

[JHZR2]

Looking to buy a vac pump for both my vehicle work as well as to install a mini split AC in my house.

Im looking at US made pumps, and the yellow jacket bullet looks like a good option... But I can get the 7 CFM version cheaper than the 3CFM. I would prefer 3 CFM I think...

Ive read that pulling vacuum too fast can freeze moisture in the system rather than boiling/evacuating. I dont want that. For a split with 50' of line it may not be an issue, because the systems come precharged so Im just pulling on the lineset, but for a car it may be way overkill...

Thoughts?

Thanks!

 

[kschachn]

There will be no difference between those two pumps for HVAC use. When you are pulling a vacuum through that long skinny yellow hose, the hose is your limiting factor. I could hook up that same hose to one of the massive mechanical pumps attached to a big diffusion pump and the result would be the same.

You can create ice sure but that is due to the ambient temperature and the final pressure. Besides, you shouldn't ever have that much moisture in a sealed system. And if you do create some ice it will sublime soon enough. Just make sure you run the pump for a good while as is always directed.

Originally Posted By: JHZR2
Looking to buy a vac pump for both my vehicle work as well as to install a mini split AC in my house.

Im looking at US made pumps, and the yellow jacket bullet looks like a good option... But I can get the 7 CFM version cheaper than the 3CFM. I would prefer 3 CFM I think...

Ive read that pulling vacuum too fast can freeze moisture in the system rather than boiling/evacuating. I dont want that. For a split with 50' of line it may not be an issue, because the systems come precharged so Im just pulling on the lineset, but for a car it may be way overkill...

Thoughts?

Thanks!

 

[eljefino]

Originally Posted By: JHZR2

Ive read that pulling vacuum too fast can freeze moisture in the system rather than boiling/evacuating. I dont want that.

That sunk the Thresher.

 

[JHZR2]

Originally Posted By: kschachn


You can create ice sure but that is due to the ambient temperature and the final pressure. Besides, you shouldn't ever have that much moisture in a sealed system. And if you do create some ice it will sublime soon enough. Just make sure you run the pump for a good while as is always directed.


My concern is when I install the lineset for the 410A system on the mini split. Notionally it will have ambient moisture in there, and given NE summertime, that could be a lot... But time is on my side too, i guess. Nothing says i cant pull vac for hours and hours to sublimate the ice, right?

On an auto AC if I opened the system to service it, there definitely would be a ton of moisture. I suppose if I left the schrader in place, at least at first, that would serve as an even greater restriction than the yellow hose...

 

[yonyon]

Icing isn't going to be a problem. If you could pull 95% of the air out of the system in 5 seconds, yeah, it would be a concern in cool weather. Even if you can pull the air out that fast you can touch the valve, feel that it's awfully cold, and make sure it reaches something close to ambient temperature then vacuum for at least another 20 minutes.

Choose the pump that can pull the lowest regardless of how fast or slow it works.