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Thread: air comp on ISX

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    air comp on ISX

    Ok here is my problem. I have a ISX in a 05 Volvo day cab. Its not making air very well. At idle it will actually lose air press. It will build up at a fast idle but is slow. I can not find a leak anywhere. I tried changing the gov. that made no differance. Talked to the shop they said the comp. was bad. I changed it today, still no better. Any thoughts?
    I guess I am getting what I deserve for buying a Volvo in the first place. What a pain to work on.


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    Have seen in the past the hoses which are cotton covered rubber become pourses and leak form the inside out - get a soapy bottle of water and spray onto hoses and check for bubbles also bad for it are the horton supply hose to fan tower

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    Quote Originally Posted by ranga View Post
    Have seen in the past the hoses which are cotton covered rubber become pourses and leak form the inside out - get a soapy bottle of water and spray onto hoses and check for bubbles also bad for it are the horton supply hose to fan tower

    Yep checked that as best I could, used spray bottle and a sponge with soapy water. I could not get to all of it but what I could there were no leaks. Monday I am going to make a hose up to bypass and go straight from the comp to the dryer and see if that helps.
    Thanks for the reply. Merry Christmas!!

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    Bypass the drier first and see if its plugged

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    I don't know if this is practical on this truck but we always try to disconnect the output of the compressor then also where it enters the first tank and see if there is a restriction.It is not uncommon for them to get blocked up.

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    Yes thats the plan for monday start looking for a restriction. But that still does not explain why it loses air at idle. Who knows might find a bad hose and just cant see/hear it.

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    Road Train Member chalupa's Avatar
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    Just for grins, get a psi gage and check your new / recon compressor. It's rare but it's happened. Seen cases where they forgot the piston rings so best to start at the beginning and eliminate the obvious.

    Also...you might shut her off and hook a shop comp to the truck. Be easier to find a leak especially if it's the fan hub.

    Let me know what you find...just curious.

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    Light Load Member pichu's Avatar
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    Quote Originally Posted by DL550CAT View Post
    Yes thats the plan for monday start looking for a restriction. But that still does not explain why it loses air at idle. Who knows might find a bad hose and just cant see/hear it.
    you dont hear because your motor is running when you shutoff, it you dont hear, but turn the switch ON and you will hear where its coming from, i had a leak in a valve the same of the valves of a tires but it was bigger in the pipe like 5" from the compressor

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    No my check valve must be bad cause that valve has pressure all the time. With the truck off if you push in on the valve with a small screw driver it releases air. The more I ponder it I am thinking blocked line plus a dryer that needs rebuilt.

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    Thats a test port on the discharge line is to check for pressure from the compressor. Most volvos use a meritor/wabco drier that has a spin on cartridge. Easy to change you just need a big filter wrench.

    Loosing air at idle with no leaks is not good. Run the truck up to pressure and shut it off. Wait 30 seconds and turn it back on and listen for leaks use a spray bottle with soapy water on all the lines (check the fan hub). If you find no leaks and a drier cartridge doesn't help try bypassing the drier itself. If all that doesn't help it time for a compressor.

    What we use for a spec on volvo's with an ISX for this is a time test. How fast will the truck build air from 80psi to governor cutoff pressure at 1100 rpm. Less than a minute is good, over that is a problem.

    Don't forget that a hole in an airbag will make you lose air at idle.

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