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HVAC I > HVAC Final > Flashcards

HVAC Final Flashcards

1
Q

What temp range is used for soldering versus brazing?

A

Soldering: under 800, usually 361 to 500. Brazing: over 800 to 1500

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2
Q

What causes solder to flow into the joint?

A

Capillary Attraction

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3
Q

What tools are used for soldering?

A

Propane or butane torch, flux, solder, appropriate solder tip

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4
Q

What tools are used for brazing?

A

Air-acetylene, regulator, hose, and torch with appropriate tip, silver solder, flux for high silver content

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5
Q

When soldering, where should flux be applied to?

A

The male end only

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6
Q

95/5 solder should be used

A

on the low side of the system, too low of a melting point. Also used for water pipes

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7
Q

When cleaning ACR copper tubing before soldering, a material that can be used is

A

Sand Cloth

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8
Q

Before using a voltmeter, always

A

Set the range selector to a setting higher than the voltage you expect to read

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9
Q

A gauge and manifold assembly used in refrigeration work may include

A

2 or 4 way valves, compound or standard gauge, manifold, valves and hoses, a 4 way valve design using a shutoff valve for each hose

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10
Q

A Sling Psychrometer measures what?

A

Dry-bulb and wet-bulb temps of air

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11
Q

T or F, An Electronic Charging Scale measures the volume of refrigerant flow into a refrig system.

A

F, measures by weight

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12
Q

How is ACR tubing measured?

A

OD

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13
Q

How is plumbing piping measured?

A

ID, Nominal

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14
Q

What are copper pipe gauge sizes, in order of thickness?

A

ACR, K, L, M, DWV

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15
Q

What side of a HVAC system piping should be insulated?

A

Suction Side to prevent heat absorbtion, excessive superheat

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16
Q

What is the silver percentage range for brazing solder?

A

15-60 percent

17
Q

For brazing with Air-acetylene, where is the red hose connected and where is the green hose connected?

A

Red for B-Tank, Green to oxygen regulator

18
Q

Why is Nitrogen pumped into pipes for brazing?

A

To force air out to reduce oxydation

19
Q

What factors affect Evaporator capacity, efficiency?

A

Overcharge (low or no superheat), undercharge (high superheat), dirty coils, fan speed or water flow, expansion valve starving coil, recycled air, blocked air flow

20
Q

What is the highest the water coil should be compared to the evap refrig (Approach)?

A

10 Delta T. Smaller approach, more efficient

21
Q

What is the job of the Condenser?

A

De-superheat, shed heat, subcool (5-20 degrees)

22
Q

What factors affect Condenser capacity, efficiency?

A

Recirculated air or water, fan speed or water flow, undercharge, overcharge, too high superheat

23
Q

What causes high or low superheat?

A

Undercharge, overcharge. Added resistance to heat exchange surface.

24
Q

How do you calculate the correct head pressure?

A

Condenser ambient temp + unit’s designed condense temp = Condensing temp

25
Q

What causes ice build up?

A

Low charge, failing metering device

26
Q

What is a Direct Expansion Evaporator?

A

Dry-type evap, meaning they establish superheat at the evap outlet. Normally use TXV. Used for smaller chillers up to 100 tons for modern chillers.

27
Q

What are the symptoms of an overcharged system?

A

High discharge pressure, and maybe high suction pressure, liquid slugging into compressor. Low super heat. AXV won’t have high suction pressure, due to mainaining constant pressure. TXV might.

28
Q

How does a TXV meter refrig?

A

Using a sensing bulb to monitor superheat

29
Q

How does an AXV work?

A

In reverse to TXV, works by suction pressure closing the valve during high load and opening during low load to maintain suction pressure.

30
Q

What are the box operating temps for low, med, high refrig?

A

0 and below, 35 to 45, 70

HVAC I (1 decks)

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