Fan for circulation problem

Discussion in 'Central Heating' started by Jim_WB9IXS, Feb 6, 2019.

  1. Jim_WB9IXS


    Feb 6, 2019
    Likes Received:
    I just installed a new Mr Heater Big Maxx 80000 btu furnace in my shop. I replaced a 35 year old Lennox furnace. Both are natural gas. The new unit works very well with one exception I cannot get the main fan to operate in the "circulation" mode. The manual is a bit vague however it clearly states the you use the green wire terminal on the thermostat connections to activate this feature. What it does not show is what do you connect the green wire to complete the circuit. Through much researching I have established that there is a standard for this. To use the fan for circulation you connect the green wire to the red wire using a normally open contact this completes the circuit. My Honeywell thermostat provide this exact function.

    So here is the issue.... When I close the green wire connection the fan comes on and within a several seconds the gas valve comes on and now we are in the heat mode. Just for clarification the red -white connection is open and this time. I cannot get anywhere with the people at Mr Heater. Is it possibly a jumper needs to be set on the control board to make this mode work?
    Something is wrong because the gas valve should not come on using just the green wire.

    Jim_WB9IXS, Feb 6, 2019
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