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LP Wall Furnace --- Replaced the gas valve

BoringBoring Member Posts: 26
I have an old "monkey wards" propane furnace in a cabin, replaced the gas valve(Essex TF5)... The old valve had a "low" and an "on" setting... Owners manual stated to run the valve in the "low" mode unless it was really cold out.

Of course the new valve is just "pilot" and "on"(white rogers 36c03-333) ... My question is the fan seems to do some strange things now...starts out at low speed, then shifts to high speed, then shifts back to low speed.... Is this normal? ( haven't ever ran this furnace before, so don't really know how it used to operate, but I have a Williams wall furnace in another cabin that acts differently)

I'm wondering if this new valve maybe a Hotter valve than the old one....? Also, I think fan operation is completely separate from the "valve".... The fan is controlled by the limit switches and the fan switches isn't it? These are temperature sensitive "snap style" limit switched ... I think.

Is there a way to adjust this thing so just the low speed fan runs or if it is really cold the just the hi speed fan runs?



  • Tim McElwainTim McElwain Member Posts: 4,358
    What is the make and model number of the fan control? The gas valve running on low would typically bring the heat exchanger temperature up to a point that the fan would kick on at low. As the valve went to high and the temperature increased the fan would switch over to high speed. With a straight gas valve the fan is going to probably work erratic. You might try replacing the fan control with an L4064A control which has high limit and fan control on the same control.
  • BoringBoring Member Posts: 26
    By the looks of the circuitry, there is limit switch that appears to be normally closed, another switch that is normally open and closes at a certain temp, then a fan switch which is normally closed to the low speed and must switch to the "hi" mode upon reaching a certain temp...the normally closed limit switch must work as a safety in the event the temp gets too hot and shuts the gas valve down. There isn't a typical fan center on this unit.
    Looks like Empire, williams and the Wards furnace all use the same circuit to control the blower fan...thermal disc style switches...I think they may be called "snap" switches...?
  • Tim McElwainTim McElwain Member Posts: 4,358
    The selector switch is a SPDT Thermo Disc type switch. It will switch back and forth from Lo to Hi based on heat exchanger temperature.
  • BoringBoring Member Posts: 26
    Great information, thanks... Maybe I should try a lower temp fan switch... This would start the fan sooner, then if the temp got hot enough to shift the selector switch to "HI" the fan would run on high, then shift back to "LO" and would run longer in the low mode before shutting off... Presently, it starts lo, shifts to hi, then shifts to lo, but only for a few seconds and shuts down... seems like it should run longer on lo prior to shutting down....a more uniform cycle...?
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