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AC pressure switch as vacuum switch

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Dodgerdoob

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Hi everyone. I have a new project I'm cooking up. I'm making a vacuum system with a Femsa ac compressor off of a Chevy 2 ton truck. This thing should really move some air. It will be powered by a belt to an electric motor. The suction line will run to a balance tank, probably made of 4" PVC. That tank will have a vacuum guage and a clean out and of course an outlet to the vacuum system. Now the goal is to maintain 14 hg from the pump and tank. The super simple way to make all this work is to spot weld the compressor pulley and clutch together and put a vacuum relief valve in the balance tank. The valves are about $16 from Grainger. But, the coil on the compressor works and energizes when connected to 12v. So for sheer gadgetry, I was wondering if there was a way to put a pressure switch to the balance tank that could de or re energize the coil as vacuum pressure dictates. I know that a lot of ac pressure switches are adjustable, but is there a way to modify one for vacuum. Or is there another device that can open or close direct current based on vacuum? Thanks
 
Most AC switches are just pressure, there may be some out there that are on the suction side, but still don't think they'll be a vacuum switch.

But you can buy vacuum switches reasonably easy and cheap.

And maybe you know, there's usually oil in the AC system that is also used to lubricate the pump itself, so if it's not one of those old piston style you may be looking for a short life so and switch would extend the life by a little :)
 
In the research I've done, Femsa was just a York copy. This thing is huge. It pumps correctly (suction is always suction) no matter which way you spin it. It has a bolt on either side that I can remove and it has oil inside so I'm just guessing its lubricated by its own reservoir rather than by the coolant. You're exactly right that a vacuum switch would prolong pump life rather than welding the clutch and pulley. I actually hadn't thought about that aspect. So what would this vacuum switch be called? My searches keep coming up with switches that open or close vacuum, not open or close circuits. Thanks for the reply.
 
Sorry never looked it up initially since i wasn't at my computer when I initially replied. But that pump should be good for what you needed, since in the day of ol' (maybe currently too) off-roaders used that style pumps as on board Air compressors to power Air tools and re-inflate their tires and the like. I believe some had them on Pressure switches too so they'll cycle as needed!

also they are just called Vacuum Switches, And i quick google search resulted in alot of choices and style, Cole Hersee makes a few (sadly not to your needs), **broken link removed** has a Vacuum Switch to, and is adjustable!

I knew of a few other companies that may sell them, but they escape me
 
I found an adjustable Airtrol switch on ebay. Should work exactly how I want. I'll just have to decide if I want to wire it NC or NO. I guess that will depend on how well my pump and seals are. Thanks for your help, 91 XR7.
 
I would say wire it normally closed so it breaks the contact at the correct pressure.

And run it through a relay, std 30 amp should be okay.

Also not a problem, electronics I'm so-so at if I have guildence but coming to wiring up cars I'm pretty good at and like it :). Then again it is what I do for a living :) (make custom harnesses for custom made cars)
 
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