Originally Posted by
54regcab
.Do you not believe that any furnaces disconnect the power to the thermostat when they reach high limit?
There were a lot of your earlier model furnaces prior to the 90's, that were the old draft box/hood style that the high limit did "depending on the fan limit" shut the high power leg to the furnace, but most were wired to open the low voltage. I have not really looked at the schematic you posted, but with 99.99% of all the newer furnaces, if the power were taken out with a open high limit, how would we be able to read the trouble codes when the tech arrived? I will say this. I have yet to run across any newer furnace that, unless the breaker was tripped, or maybe a bad low voltage transformer or door switch, that the board was not still active in the circuit upon arrival. I can't get into it on this forum, but trust me if your stat only needs 24v to keep it active, I could personally wire it using the same furnace transformer, to were unless the low voltage transformer was fried, it would stay powered regardless of the limits or the board being out.
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