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I recently came across someone who was throwing away an old craftsman air-tank and compressor. They claimed the compressor did now work anymore as it would never build pressure.

I had an old compressor laying around from project involving an airhorn. I understand that the compressor I have is not necessarily made for the purpose I intend but I had it laying around and thought I could simply remove the old compressor, replace it with mine, rewire it and call it a day.

The compressor for the airhorn has only a power and ground while the 3-prong has white, black and green. From the compressor I ran red (power) to the black on the 3 prong, capped off the white (neutral) and connected both grounds (green on the 3 prong and black on the compressor) to a bracket I had to attach to the tank. Plugged it in and nothing works. The compressor worked before I pulled it off the truck.

Any advice? Did I wire this correctly?

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    Capping off the neutral doesn't seem right.
    – JACK
    Jan 24, 2021 at 19:02
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    When you say, "pulled it off the truck", do you mean that it was wired into the truck's 12v dc power? And are you now connecting 120v ac?
    – Aloysius Defenestrate
    Jan 24, 2021 at 19:08
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    @JACK ...because it's wrong. On the other hand, airhorn compressor off a truck probably expects 12 or 24V DC, not 120V AC so theres a whole world of reasons not to work here. And by now the magic smoke may have been let out.
    – Ecnerwal
    Jan 24, 2021 at 19:08
  • Honestly that was not something I contemplated with it being 12volt and that is more than likely my issue. When they told me they chucking it in the trash my first thought went repurposing the old compressor I had, completely neglecting the fact that it was 12volt.
    – Devin Melo
    Jan 24, 2021 at 19:14
  • @Ecnerwal Sunday's my day to be sarcastic.. :-)
    – JACK
    Jan 24, 2021 at 19:36

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No, and the dead giveaway is the colors of wire on the former compressor.

Red and black are colors used for low voltage wiring on vehicles. Black is the normal current return path. And because vehicle 12V/24V is not particularly dangerous, they just use the vehicle chassis as the current return path. There is no safety ground on vehicle wiring. The thing you call "ground" is in fact the current return (negative usually).

Black and white are colors used in AC "mains" 120V power. Black is "hot" and white is "neutral". Neutral is a concept new to you: It is the normal current return path, but it is separately wired, insulated, and treated same as a hot conductor. Because 120V is dangerous.

Then there's a totally separate safety ground, which handles ONLY fault currents. Nothing should ever be electrically connected to this; it only handles current during emergencies.

So because of the way the term "ground" is used in different environments, you got different things confused.

However, the big mistake was connecting a 12V or 24V compressor to 120V and expecting the electricity elves to take care of making that work.

That compressor is fried. It's a goner.

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  • I understand now, I appreciate the info! Guess it was wishful thinking I could repurpose trash.
    – Devin Melo
    Jan 24, 2021 at 19:41
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    I'm a member of "smoking meat" on Facebook. If the tank is large enough, lots of guys cut it up, make a lid, add a side burner and turn it into a smoker. You won't get any money for it, but if usable, better than tossing it. Or at least bring it to a scrap metal dealer for recycling.
    – George Anderson
    Jan 24, 2021 at 19:53

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