Basic Gas-Fired, Forced-Air Heating Systems Flashcards
The safety gas valve provides for:
100% shutdown
The electrical energy for operating the power unit in a combination gas valve comes from the _____
thermocouple
The solenoid valve is ___ acting and requires _____ to operate
fast, electrical energy
What is the recommended setting for the blower motor to turn on?
49 - 60 degrees celsius
What is the recommended setting for the blower motor to turn off?
32 - 38 degrees celsius
How does a thermocouple opearte as a flame proving device?
It provides the energy to hold the power armature coil in. If the pilot goes out the thermocouple no longer provides any energy, so the power unit plunger releases aand closes the gas valve
How does the open circuit test differ from the closed circuit test?
open circuit is performed without power
In a deomestic furnace (under 400,000 BTU/h), the thermocouple shoudl respond to a flame failure within ____ minutes
3
How can we verify that the thermocouple responds to flame failure within the specified time?
by doing a response time test
What device may be connected in the 24 V circuit or in the 120 V circuit of a domestic furnace?
high limit switch
What is the recommended setting range for the high limit setting?
80 - 120 degrees celsius
Why is it not recommended to use a 120V thermostat in a 24 V system?
because it won’t be as accurate and the temperature differential will be greater
Are wiring diagrams the most useful for troubleshooting control circuit problems?
no
schematic
In a 24 V control system, which components may be found in the 120 V circuit?
fan, fan control, high limit, transformer
A fan OFF setting is reached and shuts off. 30 seconds later it restarts even though the burner is off. What is this condition called?
fan cycling
