HVAC II Mid-term Review

Question 1

What occurs if the HSI fails to light?

Answer 1

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

Question 2

Name the types of gas burners.

Answer 2

Drilled Port, Slotted Port, Ribbon, Single Port

Question 3

What is the purpose of the gas regulator?

Answer 3

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

Question 4

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

Answer 4

3 - 3 1/2” in. WC

Question 5

What is a thermocouple?

Answer 5

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.

Question 6

How do UV clean the air?

Answer 6

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

Question 7

How is radiant heat transferred?

Answer 7

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

Question 8

How is electric baseboard heat transferred?

Answer 8

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

Question 9

How does an EPR work?

Answer 9

“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.

Question 10

How does subcooling affect refrigerant system?

Answer 10

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

Question 11

What material is used for electric heat elements?

Answer 11

Nichrome or Nickel Chromium

Question 12

What is the Limit Switch function in electric heating systems?

Answer 12

Shuts off gas valve in case of furnace overheat

Question 13

What unit is gas pressure measured in?

Answer 13

in. WC. 1psi = 27.7 in. WC

Question 14

Where is the oriface located?

Answer 14

In a fitting called the spud.

Question 15

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

Answer 15

Hot flue gas and natural convection to vent quickly.

Question 16

What is the purpose of a sequencer?

Answer 16

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

Question 17

What does the proper gas flame look like?

Answer 17

Well defined blue with slight orange tips.

Question 18

What are the types of fan switches?

Answer 18

Temperature control or Time delay

Question 19

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

Answer 19

Yellow tips

Question 20

What are the basic furnace types?

Answer 20

Upflow, Low Boy, Downflow, Horizontal, Multipoise

Question 21

How does the EPR operate?

Answer 21

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

Question 22

What is the purpose of a CPR?

Answer 22

Keep low temp compressor from overloading on hot pull down.

Question 23

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

Answer 23

90 to 120 seconds

Question 24

What are the two pressures sensed for net oil pressure?

Answer 24

Oil pump discharge pressure - Crankcase pressure = Net oil pressure

Question 25

What is the purpose of the receiver?

Answer 25

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

Question 26

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

Answer 26

1/4" per foot

Question 27

What is the purpose of the draft diverter?

Answer 27

Reduce pilot flame blow out and main burner flame being altered

Question 28

How does the CPR work?

Answer 28

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.

Question 29

Typical comfort for people?

Answer 29

75 degrees, 50 percent humidity

Question 30

What are the methods for low ambient head pressure control?

Answer 30

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

Question 31

What is the purpose of the suction line accumulator?

Answer 31

To store liquid refrigerant that was not evaporated in the evaporator, prevents slugging.

Question 32

What does the limit swich do on a gas furnace?

Answer 32

Closes the gas valve if the heat exchanger overheats

Question 33

What does air restricted flame look like?

Answer 33

Yellow tips

Question 34

Which is heavier, air or NG?

Answer 34

Air 1.00, NG 0.60 specific gravity

Question 35

Define ventilation.

Answer 35

Process of supplying and removing air by natural or mechanical means to and from any space.

Question 36

How does an ion generator work?

Answer 36

Charge particles in a room, which are attracted to walls, floors, etc. May have a collector that collects particles.

Question 37

What is the advantage of HEPA filters?

Answer 37

Highest degree of filtration 20-30 microns. High efficiency. 99.97% of particles removed.

Question 38

What is formaldehyde?

Answer 38

Chemical used in building materials and some household products. Contains combustion gases.

Question 39

How does a Bypass Humidifier work?

Answer 39

Difference in pressure between supply (warm) side and return (cool) side. Difference in pressure between two plenums draws some heated air through humidifier to return duct and is distributed through house.