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Thread: Fan Clutch Solenoid issue

  1. #1
    Corporal wyocommo's Avatar
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    Default Fan Clutch Solenoid issue

    Spent the afternoon troubleshooting why the fan clutch does not engage at proper temp. Clutch is working as advertised when air is removed.

    When power is removed from quick exhaust solenoid it does not exhaust air in the clutch circuit to allow the clutch to engage.

    Dismantled solenoid and cleaned, appears to be OK.

    Reinstalled but no joy. If engine is stopped and air system pressure begins to bleed off it will eventually exhaust as it should.

    My conclusion is either a bad solenoid, which it sure doesn't look bad, or way too much pressure on the wet tank output air circuit.

    Could not locate the specified pressure required out of the protection regulator on the wet tank.

    Does anyone know what the protection regulator pressure output should be???

    I did a quick disassembly on the regulator and it appeared OK.
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    4 Star General NDT's Avatar
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    Did you ohm out the coil?

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    4 Star General Steel Soldiers Vendor Suprman's Avatar
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    The tm has troubleshooting step by step check this check that flow chart. Even the army techs I ask say the same for the first gen lmtv trucks. Follow the tm. I have to do it next week myself I have one that starts fine if I jump the starter relay but does nothing from the push button. The A1 trucks have good computer diagnostics plug in and run the program.

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    Corporal wyocommo's Avatar
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    Dont think it will matter in this situation. No power is applied to the solenoid when it engages the fan clutch. The solenoid is normally powered up to pass air to the clutch to keep it from engaging. This problem is occurring when the solenoid is powered down.

    It is a block and bleed function where it blocks the supply pressure and then bleeds the output going to the clutch to cause it to engage. It is not releasing the down stream pressure going to the clutch until some of the supply side pressure reduces when the engine is stopped. It should release it immediately when the solenoid is powered down.

    Pretty much must be a defective unit since it says it is rated for 140 psi. No way the wet air is that high of a pressure.
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    Air keeps the fan off no air th fan should come on. Reverse from the m939 trucks. Maybe it's something that can be taken apart and cleaned maybe a line has some gunk blocking it.

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    Corporal wyocommo's Avatar
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    OOO Kaay_ Dismantled fan clutch solenoid for the third time. This time I put a tiny bit of 30 weight motor oil on the rubber pads that seat on the cones at each end of the solenoid. Magically, the solenoid is now operating as advertised.

    A good friend once told me that EVERYTHING works better with lubrication,,,,, looks like he was right again
    There are 3 possibilities in any project
    1. You can have it FAST
    2. You can have it WORK
    3. You can have it CHEAP
    YOU GET TO PICK ANY TWO

    M35A2 has new home
    M35A3 has new 18K ELECTRIC winch
    M1078 LMTV is WAY COOL and It now has a winch
    M1082 LMTV Trailer
    M931A2 Gotta have a way to move everything! Now I need trailer.........
    M934A2 A real Wyoming style RV

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    I think mine is having a similar problem. I took the solenoid apart, and there isn't much to repair with it. I put it back together and started applying power repeatedly using a couple jumper wires. I could then start hearing a faint clicking when power was removed, but I had to have it right by my ear to hear it. Also, when I disconnected one of the air lines, air pressure released, so I'm pretty sure mine was not releasing the pressure. Now when I first crank the truck (cold), the fan turns and pulls a lot of air, until air pressure builds and the clutch disengages. I'm hopeful that it will operate correctly now, but I need to drive it around during the heat of the day to try and confirm.
    1993 Stewart & Stevenson M1078 w/wn

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    PARKER 8204 0459-45 24V-DC SOLENOID VALVE D445718 fit with no modification and cost me $37.00 on flee bay

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    Corporal wyocommo's Avatar
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    An easy test for the function of the solenoid only is to start the truck, let it run and wait for the fan to disengage when air pressure builds to normal. If you then shut the truck off, which kills power to the solenoid, you should immediately hear the solenoid vent the air that is in the line going to the clutch.

    My solenoid would not disengage until some of the air pressure bled off of the supply in the wet tank.

    As an FYI, my solenoid was the Berkert 0301 unit. I think other suppliers were used also but any block and bleed function unit with 24 volt coil should work.
    There are 3 possibilities in any project
    1. You can have it FAST
    2. You can have it WORK
    3. You can have it CHEAP
    YOU GET TO PICK ANY TWO

    M35A2 has new home
    M35A3 has new 18K ELECTRIC winch
    M1078 LMTV is WAY COOL and It now has a winch
    M1082 LMTV Trailer
    M931A2 Gotta have a way to move everything! Now I need trailer.........
    M934A2 A real Wyoming style RV

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    My fan clutch was working fine, now it appears to be non-op.

    If I'm following these threads correctly, when the truck is shut down and air has bled off, the fan should not rotate freely? If I crawl under and push on the fanwhen the truck has been sitting, the fan turns freely.

    So, when first started it should move air until the system airs up and then it will 'freewheel' until the temp sensor activates the solenoid and bleeds the air off?

    Naturally, I'm hoping this is an easy fix.. Ideas anyone? Thanks in advance..

    Pointman

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