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Thread: A/C boost vacuum solenoid retrofit successful

  1. #1
    LXi User AC439's Avatar
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    A/C boost vacuum solenoid retrofit successful

    I just did a A/C boost vacuum control solenoid retrofit and it works perfectly. Found one on Amazon for around $10 (part # X001KOG5SH). Only problem is the new vacuum solenoid has to be placed outside the mystery box.
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    Dr_Snooz's Avatar
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    Re: A/C boost vacuum solenoid retrofit successful

    Why is this needed?
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


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  3. #3
    LXi User AC439's Avatar
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    Re: A/C boost vacuum solenoid retrofit successful

    This is a follow up to my previous post (well, been 2 years) about no a/c idle boost. Troubleshooting pointed to the bad solenoid and parts obsoleted as well as no junk yard here to scout for part.

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    Re: A/C boost vacuum solenoid retrofit successful

    Can you elaborate more? That system is a mystery to me. As far as I've always known, the boost is controlled magically by the ECU. You're saying there's a solenoid, just like on a carb car?
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


    1989 Honda Accord LX-i Coupe, 220k miles, MT swap, rear disc swap

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    LXi User AC439's Avatar
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    Re: A/C boost vacuum solenoid retrofit successful

    I have a FI car. My understanding is when the A/C switch is pressed. The ECU knows it and will energize the A/C idle boost solenoid (inside the mystery box). Once energized, the solenoid will allow vacuum to vacuum line 19, which connects to the A/C idle boost valve (mount on the intake platnum, adjustable for boost level). When vacuum is applied to this valve, it will open and allow more air going from the air filter housing into the intake manifold therefore raising the idle a little bit. All this will happen 400 ms before the AC clutch engage.
    Last edited by AC439; 03-16-2019 at 06:36 AM.

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    Dr_Snooz's Avatar
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    Re: A/C boost vacuum solenoid retrofit successful

    Why is none of this in the manual???? Arrrrgh.

    Thank you, BTW.
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


    1989 Honda Accord LX-i Coupe, 220k miles, MT swap, rear disc swap

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    LXi User AC439's Avatar
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    Re: A/C boost vacuum solenoid retrofit successful

    I found out the "stuffs" inside the mystery box varies with different years / models / regions so there is never an accurate one for my LXi. I traced the electrical and vacuum to figure this out.

    There are a total of 3 vacuum control solenoids inside that box for my car. One is for A/C idle boost control, second one is for the extra 4 degrees ignition timing advance when car is cold (connects to the outer port of the vacuum advance), third is the idle boost when the A\T is in gear so car will not stall out sitting in front of red light while stepping on the brake. There is a check valve and some kind of device to maintain a constant vacuum before applying to the devices. This box is a complicate implementation IMHO.

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    Dr_Snooz's Avatar
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    Re: A/C boost vacuum solenoid retrofit successful

    Quote Originally Posted by AC439 View Post
    I found out the "stuffs" inside the mystery box varies with different years / models / regions so there is never an accurate one for my LXi. I traced the electrical and vacuum to figure this out.
    Well that answers the question then. It is definitely over-complicated. Those were the years when vacuum lines proliferated, just before OBD2 turned everything into sensors and wires. Now it's all networked because even the wires got too bulky.

    Thanks for sharing. For all I knew, the idle boost was controlled magically by elves and pixie dust and unicorn snot inside the ECU. That's what it sounded like in the manual at least.
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


    1989 Honda Accord LX-i Coupe, 220k miles, MT swap, rear disc swap

    Can't see my car? Install the "photobucket embed fix" Add-On in your Firefox browser.

    Shop manual downloads available here: https://www.dropbox.com/sh/vtyhl48z5...udl0xk_Oa?dl=0

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