Okay, probably a stupid question (I know, there are none) however, in the 12 volt schematic for my '83 Funlite it shows the wiring to the air compressor. My question is where is it and (other than providing compressed air) what is it used for in the trailer? There is no other reference to it anywhere else in the manual.

Just a guess but I would use it to air up tires.Sounds useful to me...But I already got a very compact Ryobi 18v air compressor that works with battery for my drill and impact driver,which are always with me

tech, I done some work on many different RVs and several different years of Hi Los and have never seen a factory installed air compressor, only a couple of self installed units. It is a good idea. Like that old salt, cva34, I carry my own portable one. Mine is a Slime complete tire repair kit. works off 12 or 120v. So if your Hi Lo is wired for it, find it or install one. You'd carry one with you so weight is not in question. Just my 2 cents.
Tree

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I don't know about Hi-Lo but some trailers had a pressurized water tank to supply water to the trailer rather than using a pump. There was an air valve that had to be used to pressurize the tank.

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I like Rich's answer here. Jack, does your HiLo have a water pump to move water from the fresh water tank to the faucets? If so, you don't have the pressurized system.

But, like Tree and cva, I carry an air compressor with me too, to inflate any tires that are low. Mine is a 120V one and I power it off my 1000W generator.

- Jack

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Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH, Progressive Dynamics Converter, Fan-Tastic Fan, LiFePO4 battery 12V DC Electrical System, SoftStartRV mounted on A/C
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Back in the day fresh water was pressurized by a compressor. Like Rich says. We went to the gas station and used their air hose at the pump island to pressurize the system typically. Then the compressor maintained a pressure head to force the water through the lines. My 1964 Holiday Rambler Trav'ler had such a system.
These were a real pain to live with. If the system was low on water and the pressure was down, the compressor would run for a long time before it reached a useful pressure (why we went to gas stations to charge the system). The demand pumps we use today are far more satisfactory.

The pressurized water system makes more sense. Mine does have a Shur-Flo water pump so that would explain why I couldn't find it! The fuse block in the wiring diagram is probably just a hold-over from that type of system. Haven't gotten to really dig into the wiring of the thing ... been raining here a lot and I'm about ready to build an ark!

I always carry a compressor in my car, so not an issue (120 psi max, think it's the slime kit as well. Has a coiled hose that's about 25 feet. Runs off the cig lighter. Thanks!