Forum Discussion

Colorado_Dave's avatar
Colorado_Dave
Explorer
Dec 05, 2020

SAIL SWITCH VOLTAGE CHECK

Hoping for help on troubleshooting a Furnace Sail Switch. Furnace was intermittently failing and now progressively worse. Blower would come on and after about 30 seconds would shut off - no audible attempt to open the gas valve nor ignite. I could see the sail switch blow over and using a skewer, I could feel the sail switch close/open when furnace was off. I finally pulled the entire furnace (Dometic/Atwood DFSD20121) and extracted the sail switch. I attached one of the leads to a 12V battery and using a multimeter, detected 12V when it was closed (blown over) and 2V when it was open (not blown over). Should I be getting 0V when open?
I know the furnace needs to have an open sail switch at the beginning of the cycle, and a closed sail switch when the blower blows it over. Could this 2V be causing my issue???
I do have a new sail switch on order but I have nothing to compare my current switch to. HELP!
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Dec 06, 2020
    It should be zero but your meter is what we call a high impedance load (means it is a very tiny load) so if there is any leakage due to moisture on the wires, or perhaps a leaky transistor on the control board it will detect SOME voltage.. I doubt 2 volts is a problem (but may be wrong)

    It is possible you have a control board problem... But you are not yet at diagnostic level IF, and I stress IF, you have a control board problem may I recommend Dinosaur boards.. Very well built.
  • DrewE's avatar
    DrewE
    Explorer II
    Dec 06, 2020
    Checking the switch with the voltage setting on a digital multimeter with nothing else connected (other than the 12V supply) is tricky because the multimeter has a high impedance input, and any stray voltage, capacitance, etc. can cause misleading readings. More useful is to check the switch with the resistance setting, with no battery or power supply attached. It should read an open circuit (i.e. infinite resistance) in one setting and a short circuit (a fraction of an ohm reading, usually) in the other setting.
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Dec 06, 2020
    When Sail Switch is OPEN should be ZERO DC Voltages on output side (to Limit Switch)

    Sail Switch is a 'micro switch' and do fail, hang up, get dirty etc

    Atwood AFS wiring on pg 7

    Fan starts then shuts down 30 seconds later......W/O any attempt at ignition?

    After start of fan.....
    15-17 second purge cycle
    Then Circuit board should be sending DC to gas valve and spark electrode for ignition
    No attempt at ignition ...circuit board shuts fan off


    Sounds like Circuit Board issue
    See pg 30 for Sequence (AF Models have the use circuit boards with blower relay/control incorporated on circuit board)

    ANY Error Codes.....Blinking light on circuit board??
  • enblethen's avatar
    enblethen
    Nomad
    Dec 06, 2020
    Could be a poor connection in the 2 volt side of switch. Voltage you are seeing can be simply induced.

About Technical Issues

Having RV issues? Connect with others who have been in your shoes.24,209 PostsLatest Activity: Feb 27, 2025