1989 R3500 Dual Battery Question

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89square

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New York
First Name
Willy
Truck Year
1911
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Truck
Engine Size
111
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.

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chengny

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1986
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K3500
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350/5.7
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.

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.

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75gmck25

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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
 

89square

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111
Thank you both for the info, this all makes sense!
 

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