# Gast Vacuum pump & Square-D Switch install



## CFreeman54 (Jan 14, 2009)

I am trying to install a Gast vacuum pump and Square-D Vacuum switch, and despite reading various posts and webpages, I am still a bit unclear about it. I'm sure after you have done it once, the rather superficial directions provided with the pump/switch and online are adequate, but for a first time, they seem to not be enough for me, or perhaps I am being dense. 

I think I basically understand how the vacuum hose connects between the pump, switch, reservoir, and car brake booster (probably), but I am baffled on how the switch controls the pump, and the wiring involved. In fact, I see no place to attach wires to the square-D switch. The wiring diagram that came with the switch looks nothing like the switch, and is rather cryptic anyway unless you are an E.E. used to reading such things. 

Would someone who has used these components be kind enough to walk me through this installation step by step?


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## dimitri (May 16, 2008)

You have to take the cover off the switch to see terminals.

You basically use 2 NC terminals ( Normally Closed ) in series with the red wire from the pump to the source of 12V aux power in the car. When vaccum reaches preset value NC contact is open and power to the pump is interrupted.

Black wire on the pump goes to the ground.

Most likely you will need to adjust vacuum level, so keep the cover open until its all done.

You could post a pic of the switch with open cover for further instructions or directions.

Hope this helps.


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## CFreeman54 (Jan 14, 2009)

Thanks Dimitry. I thought it must open but since the knob/nut on the back was indicated to be the vacuum pressure adjustment I was hesitant to start turning it excessively to try to remove the cover. Apparently it is the inside nut on that threaded rod that adjusts the vacuum, not the outside one visible when the case is closed.

Do most people just drill a hole in the case for the wires to exit? There seems to be no predetermined route for them. I will give the wiring a try and post a picture in a few days. Thanks again.


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## dimitri (May 16, 2008)

There are several SquareD vacuum switch models, not sure which one you got, but there should be no need to drill anything. My switch has a standard hole for electrical conduit, I guess yours must have something similar. Again, picture would be helpful.


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## CFreeman54 (Jan 14, 2009)

Thanks Dimitry. I am posting some pics of the Square-D switch and Gast pump.


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## CFreeman54 (Jan 14, 2009)

Here are some pics of the Sq-D switch and one of the Gast pump.


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## dimitri (May 16, 2008)

This model is a bit different from mine, but I can see the punch out hole in the pictire for the conduit, so you just punch it out, no drilling required.

You need to identify a pair of terminals from those 4 available which are normally closed and open when vacuum is reached. It should be in the document, or you can just test with ohmmeter which 2 terminals show zero resistance and then test same terminals after the switch trips.

Hope this makes sense, ask more questions if something is still unclear.


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## CFreeman54 (Jan 14, 2009)

That "punch out" area in mine seems pretty sturdy. I think if I punch it the rest of the case may break. Anyway, I suppose it is a good place to make the hole, one way or another. 

I will check the diagram, keeping your words in mind. I'll post more pics or ask questions when I get some wires connected. Thanks again.


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## dtbaker (Jan 5, 2008)

I have a page covering my install at http://www.envirokarma.org/ev/06.VacuumSystem.shtml and some detailed pictures in the gallery, but I don't think I took detailed pix of the wiring under the sqaure D cover.... perhaps I'll go back and take some because I remember having some questions interpreting the schematic myself. 

I went off UNswitched 12v power because I wanted the pump to be able to operate after I turned the key off.

I did a little search, and found the thread:
http://www.diyelectriccar.com/forums/showthread.php?t=24084&highlight=vacuum


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## CFreeman54 (Jan 14, 2009)

Thanks for the links DTBaker. Yes, pictures of wiring would be a nice addition. Everything I could find on peoples websites, blogs, etc. was rather vague...helpful if you kind of already know what you are doing, but not specific enough for you to use as a guide for wiring and plumbing your own if you have not done it before.

Dimitri, one more question....there are two wiring diagrams (see attached pics) that came with the vacuum switch...one appears to have one switch and the other two switches. What is going on here? Are these separate external switches? I only see the 4 terminals (L1,T1,T2,L2) on the sq-D vacuum switch.


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## dimitri (May 16, 2008)

Your switch is DPST , dual pole single throw. You only really need one pair of contacts in your case, either L1-T1 or L2-T2. There is no need to interrupt both lines in a 12V circuit, one is enough. So black wire from the pump goes directly to ground ( car's body ) and red wire goes to T1 on the switch, then L1 from the switch goes to ignition controlled 12V source. Make sure to tap the 12V source which is fused with enough capacity to run pump's motor, I think up to 10A should be sufficient for Gast pump.


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## dtbaker (Jan 5, 2008)

dimitri said:


> Your switch is DPST , dual pole single throw. You only really need one pair of contacts in your case, either L1-T1 or L2-T2. There is no need to interrupt both lines in a 12V circuit, one is enough. So black wire from the pump goes directly to ground ( car's body ) and red wire goes to T1 on the switch, then L1 from the switch goes to ignition controlled 12V source. Make sure to tap the 12V source which is fused with enough capacity to run pump's motor, I think up to 10A should be sufficient for Gast pump.


only difference I did with mine is that I used the always-on 12v power from dc-dc rather than key-switched 12v; I wanted the pump to be able to finish when key was off. I have dc-dc powered 'always' so that things like clock, radio, lights work without key-on. I do NOT have an aux battery, and run directly off the dc-dc.


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