HVAC Rooftop Units Flashcards
Are rollback (temperature) switches normally open or normally closed?
normally closed
What is the purpose of the ignition transformer?
strike and arc (spark) and ignite the gas
What is the purpose of the flame rod?
The purpose of the flame rod is to prove flame. The flame provides a current path and if the current is sensed by the controller, the heating system will not lock out and shut down the gas valve.
What is the purpose of the combustion blower motor (induced draft fan)?
The combustion blower motor ensures that the flame burns properly. The blower motor must be operation when there is a burner flame.
When a rooftop unit receives a call for heat, which component should start first?
The combustion blower motor (draft fan motor)
For rooftop units that use intermittent ignition, once the pilot flame ignites, what must happen before the main flame ignites?
The flame rod senses the pilot flame.
A rooftop unit can be divided into three parts. What are these parts?
a) heating section
b) cooling section
c) ventilation section
Once the main flame ignites which motor starts?
The blower (evaporator) motor
What happens after the thermostat contact opens?
The main gas valve is de-energized and the gas flow ceases.
What is the difference between intermittent ignition and DSI?
Intermittent spark ignition ignites the pilot flame and the direct spark ignition ignites the main flame; no pilot exists
The sequence of operation for the DSI system is longer than the intermittent spark (pilot) ignition for rooftop units.
True or False
False;
The DSI sequence is shorter because there is no pilot flame.
When the rooftop unit receives a call for heat, which terminal point on the rooftop becomes energized first?
The W1 terminal
Make-up air units are normally interlocked with specific equipment. What is that equipment?
an exhaust fan motor
What is the make-up air unit’s main function?
The make-up air unit’s main function is to supply fresh outside air and to heat that air when necessary. The exhaust fan works in conjunction with the make-up air unit.
What kind of heating systems do two-wire thermostats typically control?
A two-wire thermostat typically controls home furnaces and unit heaters in garages or on commercial premises.
