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HVAC TZ > HVAC Test 1 > Flashcards

HVAC Test 1 Flashcards

1
Q

What is the purpose of the limit switch located on the heating element?

A

Limits the power. Keeps it at a safe level.

*From the blower motor shutting down, can’t get any airflow, heating element gets too hot, the house could burn down.

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2
Q

How many BTU is one ton?

A

12,000

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3
Q

Latent heat of ice?

A

144

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4
Q

What do we vacuum down to?

A

29.9 mercury

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5
Q

On the compressor and reading the resistance between run and start but read infinity, OL, common and run and common and start.

A

Open overload

*If you read resistance on the run winding then it’s not a bad winding.

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6
Q

How do you use an ammeter?

A

In series

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7
Q

What does the Delta T measure for use?

A

Return air and supply air

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8
Q

What is an EMF meter?

A

measurements of ambient electromagnetic fields that are performed using particular sensors or probes.

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9
Q

What keeps the compressor running cool?

A

Cool Suction line vapors

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10
Q

What does OL mean?

A

Openline, Open circuit

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11
Q

The winding on the motor are located where?

A

Stator

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12
Q

What component will energize the compressor located in the condenser?

A

Contactor

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13
Q

What kind of heat makes a face change but no change in temperature?

A

Latent heat

*Latin for hidden. Hidden from the thermometer.

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14
Q

42,000 of BTU is how many tons?

A

3.5 tons

*12,000 BTU’s = 1 ton
42,000 / 12,000 = 3.5 tons

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15
Q

What is a sensible temperature?

A

The temperature that we can measure.

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16
Q

What is the CFM per ton?

A

400 CFM per ton

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17
Q

How many BTU’s do you have to remove from the air to face change?

A

970 BTU per lbs.

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18
Q

Any capacitor run or start is always in what with its windings

A

In series with the start windings.

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19
Q

Any time you use an ohm meter the power must be set to?

A

Off position

20
Q

What kind of magnites to you form when you use electricity?

A

Electromagnites

21
Q

When your not calling for cooling on a thermostate between R and Y you are reading what voltage?

A

Low voltage, 24V

*Except when you are working with refigeration, then you might be dealing with 120 or 240V

22
Q

How do you condemn a proper grounded compressor?

A

Put one lead on any terminal and one on the interconnecting piping (copper).

23
Q

On the compound gauge, on the low side, what does it measure?

A

It reads above atmospheric pressure (14.7psi)

Low side pressure, Atmospheric pressure, vacuum.

24
Q

When the liquid refrigerant leaves the condenser and enters into the TXV or any metering control it will enter into the____?

A

evaporator coil

25
Q

What do we always purge from our manifolds?

A

No condensable air

26
Q

What is Alternating Current (ac)?

A

Electric current in which the direction of electron flow reverses or switches at regular intervals. 60Hz current, electrons reverse direction 120 times per sec.

27
Q

How do you measure superheat?

A

Take the suction line pressure, convert it to temperature minus the actual suction line temperature.

28
Q

How many terminals for a hermetic compressor usually have and who are they?

A

3 terminals

1)R-Run 2) S-Start 3) C-Common

29
Q

How many windings does a hermetic compressor have?

A

2

30
Q

How many windings does a 3 phase motor have?

A

3

31
Q

If you Ohm the windings of a 3 phase compress, how would they Ohm?

A

The same. 120 degrees apart.

32
Q

We use current relays to de-energize start windings and start capacitors. What are other relays used?

A

Potential Relay also is known as a voltage relay.

33
Q

Two ways a compressor can fail?

A

Electrical and mechanical.

34
Q

What do you have to do for the refrigerant to change its physical state?

A

Add or remove heat

35
Q

What is thermodynamics rule #1?

A

Heat is work and work is heat

36
Q

What is thermodynamics rule #2?

A

Heat travels from hot to cold.

37
Q

What are the terminals of a termostate?

A

R-Power G-Fan W-Heat Y-Cool C-Common

38
Q

How do you wire a potential relay?

A

5-2-1

1) 5 to Common terminal to the compressor
2) Common terminal to compressor
3) 2 to Herm (Start winding) of the capacitor
4) 1 to Start capacitor

Make sure the common to the terminal of the compressor and 5 of the potential relay are both on the same side of the contractor.

39
Q

Heat can transferred or moved from one body to another by?

A

Radiation, conduction, or convection.

40
Q

What is the most common case for a transfromer to burn out?

A

Shorted low voltage

41
Q

What has a primary in and secondary out?

A

transformers

42
Q

How do we measure capacitors?

A

Using MFD milliFarad

43
Q

What does NC mean?

A

Normally Closed

44
Q

What does NO mean?

A

Normally Open

45
Q

A motor that uses a run capacitor in series with a start winding without using a start capacitor is a?

A

PSC - Permanent Split Capacitor

note: CSCR uses a start capacitor

46
Q

What determines the temperature at which a refrigerant will face change?

A

Pressure

47
Q

Where are internal overloads located?

A

Internally in the motor. In the common terminal of the compressor.

HVAC TZ (1 decks)

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