Polarity

Empire_2

Here is how you check.

big willy

polarity

I had two of my guys install a furnace two winters ago. It is a Trane two stage condensing. Today I went to a service call and the controll was flashing reversed polarity. I checked it and it was backwards. I have never seen a modern furnace work with the polarity reversed. I thought the flame rectification system would not allow this. Now two years later it wont run even with the proper polarity. I am getting a new board from the dealer tommorow. I guess I dont fully under stand how flame rectification works. I would have thought running at all was not possible but here I sit.

[Deleted User]

here's the science

from lochinvar

Reverse polarity? So what really happens when polarity is reversed on a EWN, TNR or EP. Typically a unit
will fire and maybe even run, but intermittent problem are likely to occur. All three of these units use a hot
surface ignition system which is dependent upon flame rectification. The Turbo Charger and the Energy Rite
both use an igniter that is accompanied by a flame rod. The Efficiency Plus uses the PLT3400 igniter, which
is the igniter/flame rectifier combination.
The basics of the flame rectication process are pretty simple. After the ignition module goes through the
ignition sequence it sends an AC signal to the flame rod. Due to a de-ionization process that occurs when the
flame contacts the flame rod, a small DC micro-amp current is produced. This current is what the module
looks for to prove the flame. Typically the signal will need to be a minimum of a .5 micro amp for the module
not to lock out.
So what does polarity have to do with this? When polarity is reversed on the unit the flame rectification
process is altered. Now that the power leads are switched voltage is being “pushed” through the chassis
instead of “collected” by the chassis. This reverses the de-ionization process, causing the DC micro amp
signal to be too high. The ignition module receives this high micro amp signal and locks out because it senses
a short.
This same principle applies to all hot surface ignition systems. So the next time you troubleshoot a unit that
has locked out due to flame failure, don’t forget about the possibility of reversed polarity.