07 Kenworth T800 AC Fan and Binary Switches

Discussion in 'Kenworth Forum' started by Lowboy456, Apr 21, 2021.

  1. Lowboy456

    Lowboy456 Light Load Member

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    Hi folks! I was wondering if anyone can tell me... I think I have this right from bits and pieces I can gather on the web about the fan and Binary switch. Its so hard to find schematics for my particular system let alone how it functions from fuse to relay to compressor through the switches and so on.

    Is it correct that the binary switch by itself cuts the AC compressor on and off and has nothing to do with the fan?

    And the fan switch turns the fan on and off?
    I suspect my fan switch is cutting the fan off at too low a pressure at 150PSI high side.

    -===================================================

    1st off I have a brand new Sanden SD7 4042 Heavy Duty compressor replacing a Sanden SDH715.
    Turns out my impossible to find nightmare leak was the compressor seal. That started last summer and I winged it through the last little bit of summer adding some freon on scorcher days where I was off road in dusty conditions. This is a dump truck btw.
    I continued looking for my leak over and over all winter long here and there with no luck. I dont trust the sniffers too much. They go off too easy.

    Knowing the hot dusty days are coming I started back trying to find the issue.
    It would hold 220 PSI nitrogen for 1 hr and even gain 2 psi.
    It would hold a freezing cold charge 2 days. 3rd day it was on the way out and finally blowing hot.
    I never could find any dye around the compressor anywhere but could smell freon strongly standing on the ground that last time I had freon in that system 3 weeks ago. That's when I threw my hands up and knew it must be the compressor.

    I had the evaporator out while still hooked up taken out of its box, soaped it good while it still had low line pressure inside and no bubbles anywhere.
    That was my #1 suspect since dye had only revealed a slow leaking low side schraeder valve before.
    Fixed that still 2 days worth of air and downhill.

    =========================================================

    This compressor works very good on pressures that I've never seen on any system.
    Low side is 15 PSI
    Hi Side is 150 and its blowing ice cubes.

    When I first charged this system I had it vacuumed down to 250 microns and gave it all the freon it would take with the engine off with vacuum alone and a new 30lb R134 Jug.
    I've never seen a system not need more freon after doing it this way but this system was already over charged not much but enough to where the fan would never go off.
    It was 25 on the low just like the old and the compressor cycling on at 230 and off at 420.

    If I plugged in the compressor and started the engine the fan stayed on period even without turning the AC on. Too much pressure from over charge. With this switch 150 PSI has to be seen at some point to turn the fan off.

    The old system blew ice cubes at 25 low side and 155 high side set with fan manually on. Fan came on at 320psi and off at 150psi worked great best air I've ever seen.

    I think this fan should cut off at a good bit higher pressure than 150 PSI.
    Of course if I turn the fan off hi side pressure builds and the fan kicks on at 320 psi and drops back down kicking the fan off at 150psi. Sometimes kicking off that takes a couple minutes and sometimes not while it lingers at 150psi.


    When I adjusted last night, I vacuumed down and empty freon tank and let the pressure down to where I had 100 psi static from about 122 PSI static and then started the engine.
    I put it in a tank so I could add some back if I took to much out.

    A Sanden's article and Kenworth manual suggests 15 on low and 160ish on high and reading also on a Mustang forum is where I learned that high side should be set to twice the ambient temperature + 20% on Sanden compressors. Some suggest +30% for cold cold air on the Mustang forum.

    So then I started the engine and still had 180PSI on the high side with fan set on.
    So I let a little bit more out from the high side into my tank to lower pressure down to 161PSI which was twice ambient +20% and the fan still would never shut off.

    That's when I thought well.... the fan shuts off at 150psi so maybe I should try 150 so it has a good chance of shutting off and hopefully it will still cool.
    And it working very good at 150psi the fan is actually on/off 50/50ish depends how much air flow its getting.

    Any how I think the fan switch is out of spec but don't want to get the wrong one.
     
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  3. Rideandrepair

    Rideandrepair Road Train Member

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    Have you changed the fan switch at all? If you have the part #s of the bianary switch, and the fan switch, I can look them up. Check the specs. Dealer should have the correct switched based on vin #. Meanwhile I can check the difference between the two compressors.Some are different CCs and different amount of pistons. Shouldn’t matter though. Best way I find is to add Freon by weight. According to the I.D. tag if equipped. Binary switch is usually Lo/hi pressure switch, that controls compressor, either side of it’s dual function can go bad. From what I understand. Fan switch is a high pressure switch w/ cut in cut out ratings, but for fan only. That’s how my Freightliner is anyway. Lots of different switches, with different ratings. Don’t really know why honestly. Different size systems I guess.
     
    Last edited: Apr 22, 2021
  4. Rideandrepair

    Rideandrepair Road Train Member

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    Compressors are the same,7 piston, 155cc, as far as switches go. I see purple colored binary switch that’s normally closed, opens at 330-370, closes at
    180-240. Controls fan and high side. Maybe that’s what you have, can’t miss it as it’s purple, along with a separate low pressure switch. Instead of a hi/lo pressure binary switch, and a high pressure fan switch.Really no telling, without the year. Dealer can tell you what the correct switches are and what they do, per vin #
     
  5. Lowboy456

    Lowboy456 Light Load Member

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    I have not changed out any switches yet but will see if I can get the part numbers.

    I try to get parts if I can somewhere besides the dealer because they want 10x what the part is worth.
    It would probably cost over 200 bucks just to throw both AC switches on there from the KW dealer.

    Yea I like adding freon by weight too but my scales are broke right now.
     
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  6. spsauerland

    spsauerland Road Train Member

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    Last six of VIN and I can get switch P/N's.
     
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  7. Rideandrepair

    Rideandrepair Road Train Member

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    I have a truck air book from Truckpro, if you have one near, with cross reference , MEI will mail parts also. At least they used to.
     
  8. Lowboy456

    Lowboy456 Light Load Member

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    Ok thx! Vin is 195828
     
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  9. Lowboy456

    Lowboy456 Light Load Member

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    We have a Truck Pro and a Global parts. Also T&T Truck parts will deliver but you have to have an account setup with them. We try to avoid setting up accounts, although it saves you quite a bit of money to do so.
     
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  10. Rideandrepair

    Rideandrepair Road Train Member

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    My friends in the same boat somewhat. He’s missing a fan switch. We have it charged up, left it low. Compressors hot wired with a switch. I’m trying to figure out what the switch he has does, and what’s missing. I think I found his and yours. Wouldn’t bank on it though. Waiting to see what Spauderland comes up with. Just curious.
     
  11. spsauerland

    spsauerland Road Train Member

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    Sorry, can't look up KW parts on phone. Binary switch is P/N 79PSD4-1, MEI P/N is 1515. Fan switch is 79PSL3-4, MEI P/N 1310. Fan switch opens 280-320 and closes 250-210 is Paccar spec. Hope this helps. With R134a, 2 oz either way on charge really throws off performance. I know you know this, but scale charge is best. I always add extra 2 oz in charge for amount in hoses if they are empty.
     
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