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Electric furnace design and troubleshoot
When troubleshooting, understand you are working with potentially lethal voltages. If you do not have the ability to do these operations safely, do not attempt them.
Electric furnaces are more of a converter than a furnace. They convert one type of energy to another.
Electricity is a form of energy and the electric furnace converts electricity to heat rather than like a gas furnace that relies on a chemical change that releases heat.
The elements are where the transformation takes place.
The elements warm up and a fan moves air past them to transfer the heat to the air in the structure.
Most of these elements will glow red when the fan is off as show below.
Electricity is a form of energy and the electric furnace converts electricity to heat rather than like a gas furnace that relies on a chemical change that releases heat.
The elements are where the transformation takes place.
The elements warm up and a fan moves air past them to transfer the heat to the air in the structure.
Most of these elements will glow red when the fan is off as show below.
Electric furnaces must have some sort of switch that connects the power to the electric elements. These switches can be contactors that allow power to pass to the element when the thermostat calls for heat.
Or we can use sequencers.
Sequencers are time delay relays that begin their timing when the thermostat calls for heat. They will usually bring the elements on one at a time over a time period of 30 seconds to one minute. They will not bring on all the elements at the same time as a contactor will. Below you can see how a sequencer equipped furnace cycles on and off.
Below is a video that covers how one brand of sequencer operates.
Over the years, sequencers have changed in design. So sometimes when the sequencer needs to be replaced, the new one will not look like the old one. If you are replacing a sequencer, you need to understand how both of them sequence and where the terminals are.
The video below covers replacing the Honeywell R8330D1039 sequencer with the White Rodgers 24A34-6 model.
The video below covers replacing the Honeywell R8330D1039 sequencer with the White Rodgers 24A34-6 model.
The elements run at a very high temperature as you could see from the top video. Thus sometimes they burn up and separate. At that point, the entire element assembly can be replaced or, in some cases, the the failed element can be restrung. The choice to restring is dependent on the condition of the element carrier, availability of parts and the age of the furnace. The below video covers how to restring an electric element.
The power source for electric furnaces is of course electricity. It is not just the source of control power. That means all the energy used to heat the structure travels through the wires running to the furnace. The connections that must be made at the terminals must be large enough and above all, tight. Electric furnaces often fail because of loose connections. If the connections are loose, they will overheat and burn the wires. The video below covers how to check for burned wires.