original electric furnace

Posted on Feb 6, 2014

This is a switched system, meaning it doesn`t have a sequencer like modern electric furnaces. Instead, relays are used. Maybe this is a good upgrade to make, installing a sequencer. The blower is a 5 speed blower, although only two seem to be used (unlike what the wiring schematic says): Low speed for startup, then high speed. 5 heat strips, or `element-electric heat`, element 1&2 on

original electric furnace
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circuit breaker 1 (CB1), element 3&4 on circuit breaker 2 (CB2), and element 5 + blower motor on circuit breaker 3 (CB3). Switch K1 drives the blower motor. This is the switch that is turned on when the thermostat manual switch is set to run the fan. If K1 is OFF, and K2 or K3 is on, then the blower runs at low speed. If K1 is ON, then the blower runs at high speed. I will have to research a bit more to understand how the thermostat drives the different switches. It looks like upon a call for heat, the thermostat will close K2, which will run the blower on low speed, and energize HE1, 2 & 5. K2 AUX contact will close, possibly after a delay ( ), and energize K3, which will turn HE3 and HE4 on.

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