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1989 R3500 Dual Battery Question

Discussion in 'Electrical & Audio' started by 89square, Nov 10, 2019.

  1. 89square

    89square Junior Member

    Posts:
    13
    Likes Received:
    10
    Joined:
    Dec 25, 2018
    Location:
    San Diego
    First Name:
    Joe
    Truck Year:
    1989
    Truck Model:
    R3500 Dually
    Engine Size:
    454
    Hi,

    My truck has a secondary battery tray that was empty when I bought it, It looks like it did have one there at one point because there are battery cables ran to the location that have been taped over. From what I had read, this was to power a trailer (there is a power connector at the wheel well in the bed).

    What other items were typically powered using the secondary battery? I have a few things not working, including the AC. I noted that the secondary battery positive cable is connected to a power distribution block on the firewall, it also has a cable going to the AC relay on that same side of the block and it has me wondering if if this could be why my AC does not blow cold. I have attached a few pictures.

    Thanks.

    89_1.jpg

    89_2.jpg

    89_4.jpg

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  2. chengny

    chengny Full Access Member

    Posts:
    4,002
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    755
    Joined:
    Feb 22, 2012
    Location:
    NH
    First Name:
    Jerry
    Truck Year:
    1986
    Truck Model:
    K3500
    Engine Size:
    350/5.7
    From what I had read, this was to power a trailer (there is a power connector at the wheel well in the bed). What other items were typically powered using the secondary battery?

    In addition to trailer wiring, the system was also designed to supply power to camper equipment.

    I have a few things not working, including the AC. I noted that the secondary battery positive cable is connected to a power distribution block on the firewall, it also has a cable going to the AC relay on that same side of the block and it has me wondering if if this could be why my AC does not blow cold.

    That sounds correct. The big red lead to the A/C relay is only for blower operation. The compressor clutch should pull in - provided everything else is alright.

    aux batt.JPG
     
  3. 75gmck25

    75gmck25 Full Access Member

    Posts:
    685
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    333
    Joined:
    Oct 13, 2016
    Location:
    VA
    First Name:
    Bruce
    Truck Year:
    1975
    Truck Model:
    K25
    Engine Size:
    5.7
    The wire from the junction block to the A/C blower relay is only used for high speed on the blower, and there should be a 30 amp fuse in the line running across the firewall. The lower blower speeds go through the dash switch, but on high speed it kicks in the relay and makes a direct 12 volt connection. The relay is also used to turn the blower on high speed when you put the A/C in Max or recirculate mode.

    Bruce
     
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