Anyone here who has been a tech or works for a shop that sells these, either the insert or the freestanding units, must be all too familiar with the inevitable low limit failure.
Stove starts, goes through the start up, blower may actually come on depending upon how many times you've tries to restart and then wah wah wah...two short red blinks and the unit goes into shut down.
I haven't been to this issue in a while but Friday I went on a service call where this was the issue. I brought a new low limit switch to exchange, as I always do. I replaced the switch and the unit worked fine. For giggles, set the old switch on top of the exhaust and clipped my DMM to it.
Usually when I change out the switch, the old switch still works, but for whatever reason it don't work in the machine. Same was true Friday.
Just as I expected...both switches closed moments from each other. Resistance through each switch was close but slightly lower on the new one.
On this stove, the blue wire from the control box sends 5v to the low limit and the green wire sends 10v to the pressure switch, each switch shares a common back to the board which is a brown wire. So the board is looking for roughly 15v back and can tell which switch is failing using some simple math.
What caught my attention is that on the low limit side, we were gaining resistance with the old switch as it aged in the stove but seriously...it wasn't much, so my thought was that the brown wire running back to the board and the little pigtail that jumps over to one side of the pressure switch was very very close to the combustion blower. Not enough to burn it but certainly enough to affect the resistance in the copper wire.
My hypothesis is that the slight increase in resistance from the switch AND the shared common leads to the board are kicking out low limit codes because the low limit is the smaller value. I really have no idea what Lennox is looking for backwards, but whatever it is they should sort this out another way.
So I cut the brown wire 1 foot down from the control board and twisted up a pair of new wires to run back independently to the switches, far away from the heat, installed the old snap switch back in the machine and presto! She ran just fine. No issues.
Stove starts, goes through the start up, blower may actually come on depending upon how many times you've tries to restart and then wah wah wah...two short red blinks and the unit goes into shut down.
I haven't been to this issue in a while but Friday I went on a service call where this was the issue. I brought a new low limit switch to exchange, as I always do. I replaced the switch and the unit worked fine. For giggles, set the old switch on top of the exhaust and clipped my DMM to it.
Usually when I change out the switch, the old switch still works, but for whatever reason it don't work in the machine. Same was true Friday.
Just as I expected...both switches closed moments from each other. Resistance through each switch was close but slightly lower on the new one.
On this stove, the blue wire from the control box sends 5v to the low limit and the green wire sends 10v to the pressure switch, each switch shares a common back to the board which is a brown wire. So the board is looking for roughly 15v back and can tell which switch is failing using some simple math.
What caught my attention is that on the low limit side, we were gaining resistance with the old switch as it aged in the stove but seriously...it wasn't much, so my thought was that the brown wire running back to the board and the little pigtail that jumps over to one side of the pressure switch was very very close to the combustion blower. Not enough to burn it but certainly enough to affect the resistance in the copper wire.
My hypothesis is that the slight increase in resistance from the switch AND the shared common leads to the board are kicking out low limit codes because the low limit is the smaller value. I really have no idea what Lennox is looking for backwards, but whatever it is they should sort this out another way.
So I cut the brown wire 1 foot down from the control board and twisted up a pair of new wires to run back independently to the switches, far away from the heat, installed the old snap switch back in the machine and presto! She ran just fine. No issues.
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