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BFL13's avatar
BFL13
Explorer II
Aug 23, 2020

8531 Limit Switch Wiring ?

Am in the middle of a battle trying to swap out the limit switch from my spare 8531-lll I got from a guy, and the OEM 8531-ll in my Class C.

I managed to get at the switch in the lll, but no luck yet in the installed ll, because the squirrel cage is rusted on after I got the Allen set- screw out. Can't get at the switch with the squirrel cage in the way. (or is there another way?---??)

Assuming I ever get that solved soaked in penetrating oil spray overnight, the switch on the ll is in a different location from the lll's, which was way inside, being more up front behind the left (looking at it from outside--same end as the circuit board) end of the squirrel cage.

So besides all that, there are two wires, one to each side of the limit switch. I have not removed these on either yet, but want to know if it matters which goes where on the limit switches. If not, I can wire it up however, but if it matters which side of the limit switch gets which wire, then I will have to be careful about that if I ever get that far.

Thanks!

BTW, I have read here in previous threads, that there might be different temp range limit switches at play, so I will note any part numbers for that. I suspect if the lll is way in and the ll up front, they will experience different levels of heat?

Anyway, one step at a time--first to know if the wiring matters.

38 Replies

  • Have you tried shorting the thermostat wires together? Once shorted the furnace should run and produce heat, Separating the wires, it should go into cool down mode and shut off.
  • I got the ll's cage off, so was able to swap limit switches to test whether the OEM one is causing the problem. Nope! The lll's still does it but not as much, where it lets the temp get a bit higher I guess.

    So it is back to finding the real problem, but not for now--it is still August after all.

    Thanks again for all the help.
  • Inspect the crimp 1/4 blade connectors to insure that they are fully on exposed copper wire and not partially on the insulation.
  • Thanks, I suspected that, good to know. So my new trick must be to try the furnace with the limit switch by-passed, now I have the wiring understood, and see if it still keeps cutting in and out on the way up as it brings the RV to Tstat set temp.

    If it runs steady, then I can go ahead and put the proper size limit switch in rather than the lll's. ( I have confirmed no duct blocking with four ducts, registers open, and good return air from big enough return air opening per installation specs.)
  • 8531-ll
    High temp limit switch is 130*F (#35132)

    8531-lll
    High temp limit switch is 190*F (#37022)


    Not really interchangeable
  • Thanks for the good tips and the wiring info. You guys better not retire from rv.net or the rest of us will be stranded! :(
  • Wires can go on either side. After soaking the shaft with Penetrating oil, try to TURN the shaft using the intake burner impellor wheel. That will free up the shaft to pull the Main impellor wheel. NO, without the Impellor removed it is almost impossible to get to the Hi Limit switch and screws. Doug
  • I would try to follow the wiring diagram on page 10.
    Bryant RV service manual
    Screw on the sail switch could very difficult. My switch was on outside of housing. Broke switch then used needle nose vise grips to get screws out.

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