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Flashcards in HVAC II Mid-term Review Deck (39)
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What occurs if the HSI fails to light?

The unit will go into Safety Lockout if no ignition between 4-11 seconds


Name the types of gas burners.

Drilled Port, Slotted Port, Ribbon, Single Port


What is the purpose of the gas regulator?

Drops natural gas pressure to the proper level (in. WC) and maintains constant pressure at outlet feeding gas valve.


What is the normal gas pressure for a natural gas furnace?

3 - 3 1/2" in. WC


What is a thermocouple?

Two dissimilar metals welded at one end, HOT JUNCTION. When heated it generates small voltage, 15mV load, 30mV without load. COLD JUNCTION is non-heated side. Hot Junction heat creates voltage, opens shutoff valve.


How do UV clean the air?

UV-C light is germicidal, damages microbe DNA as air is past under it.


How is radiant heat transferred?

Travels in a straight line from source and is absorbed by solid objects that then warms the space.


How is electric baseboard heat transferred?

Natural Convection drawing air from below, which rises through the top of the unit.


How does an EPR work?

"Hold Back Valve," installed on suction line at Evap outlet. Internal bellows senses evap press. And throttles suction gas to compressor. Open on Rise of Inlet.


How does subcooling affect refrigerant system?

Increases net refrig. by latent cooling. Ensures minimal flash gas to allow maximum heat absorption in Evaporator.


What material is used for electric heat elements?

Nichrome or Nickel Chromium


What is the Limit Switch function in electric heating systems?

Shuts off gas valve in case of furnace overheat


What unit is gas pressure measured in?

in. WC. 1psi = 27.7 in. WC


Where is the oriface located?

In a fitting called the spud.


How are combustion gases removed in conventional non-eff. Furnace?

Hot flue gas and natural convection to vent quickly.


What is the purpose of a sequencer?

Low-voltage control of many heating elements, up to six.


What does the proper gas flame look like?

Well defined blue with slight orange tips.


What are the types of fan switches?

Temperature control or Time delay


What does a NG flame look like in furnace with primary air restriction?

Yellow tips


What are the basic furnace types?

Upflow, Low Boy, Downflow, Horizontal, Multipoise


How does the EPR operate?

Used for low ambient. ORI, closes when pressure drops to maintain refrig in evap


What is the purpose of a CPR?

Keep low temp compressor from overloading on hot pull down.


What is the normal time delay on oil pressure safety control?

90 to 120 seconds


What are the two pressures sensed for net oil pressure?

Oil pump discharge pressure - Crankcase pressure = Net oil pressure


What is the purpose of the receiver?

On liquid line used to store liquid refrig after it leaves the condenser.


What is the minimum slope of a horizontal run of a flue pipe?

1/4" per foot


What is the purpose of the draft diverter?

Reduce pilot flame blow out and main burner flame being altered


How does the CPR work?

CRO, throttles suction gas to compressor to keep compressor current at no higher than set point. Prevents overloading during hot pull down. High temp = high pressure = dense gas. CPR reduces pressure to compressor.


Typical comfort for people?

75 degrees, 50 percent humidity


What are the methods for low ambient head pressure control?

1. fan cycling using pressure control 2. fan speed control 3. air volume control using shutters and fan cycling 4. condenser flooding devices