JB Vacuum Pump Size?

[Nytefog]

I'm trying to decide on which size JB pump to get. It mainly used for resi and on occasion some larger commercial units, but mainly residential. I was deciding between the 1.5 and 3 CFM. o I already have a 5 CFM pump that is older and am looking to upgrade. I just don't want to get a oversized pump to reduce the risk of producing ice when evacuating...or should i get another 5 CFM....

I've read the manufactures recommendations but wanted to know what works best real work situations.

[AC5096]

I like 5's. I also have a 1.5 that sees limited use.

[jim bergmann]

There is almost no chance of freezing an A/C system with an oversize pump unless you are performing the evacuation close to or below the freezing mark. As if not more important as pump size is the hoses that attach to it. For any residential system, 3 CFM is more than enough pump.

If you are using 1/4" hoses and no core tools, it doesn't matter what the size of the pump is as you are only capable of moving about 0.7 CFM through that type of rig. Vacuum is limited by physics. -14.7 psi is the deepest it can go. The ONLY way to go faster is larger hoses.

[Nytefog]

indeed, i uses 3/8 hoses and no valve cores

[Nytefog]

There is almost no chance of freezing an A/C system with an oversize pump unless you are performing the evacuation close to or below the freezing mark. As if not more important as pump size is the hoses that attach to it. For any residential system, 3 CFM is more than enough pump.

If you are using 1/4" hoses and no core tools, it doesn't matter what the size of the pump is as you are only capable of moving about 0.7 CFM through that type of rig. Vacuum is limited by physics. -14.7 psi is the deepest it can go. The ONLY way to go faster is larger hoses.

If this is true is really doesn't matter what size pump you get? If you need a 1.5 CFM and you get a 10 its shouldn't matter as long as you have small hoses

[jim bergmann]

That is correct. You are limited by the restriction if the hoses. The vacuum is limited by physics. A 10 cfm pump will flow no more than a 1.5 cfm pump when both are attached to a 1/4" hose.