ELEC UNIT 13 Flashcards
why do oil and gas furnaces require heat exchangers but electric furnaces don’t?
this is so that products of combustion don’t enter the conditioned space
what is the heat source in an electric furnace?
electrical resistance heater
how do air pressure switches in furnaces work?
they are normally open and close when the pressure drops by the fan venting off any flue gas. I think.
what is an intermittent pilot, standing pilot, and direct ignition?
intermittent pilot burns only when there is a call for heat, standing pilot burns constantly, direct ignition ignites when call for heat (spark ignitor or hot surface ignitor).
what are the four devices to prove a pilot burner is lit, and how do they work?
liquid-filled pilot sensor (pressure inside heats up from flame)
cad cell (changes resistance in response to light)
flame rod (conducts electricity)
temperature sensor (self-explanatory)
what is a pilot assembly?
assembly that holds the pilot burner and method of ignition
what is the control of a furnace called?
furnace control board
what does the gas valve do?
opens on demand for heat to supply gas
what is a thermocouple?
used in standing pilot burners. produces small voltage when heated, which energizes gas valve.
what is the device that controls the starting of a furnace?
ignition module
what is the “heart” of the oil burner control system?
the primary control
how is oil transferred in an oil furnace?
with an oil pump
how are oil furnaces ignited?
with ignition electrodes
how does a primary control prove that the burner is lit?
with a thermal sensor like a stack switch or cad cell
what does the ignition transformer do in oil furnace?
produces spark ignition
