HVAC Test 1

Question 1

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

Answer 1

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.

Question 2

How many BTU is one ton?

Answer 2

12,000

Question 3

Latent heat of ice?

Answer 3

144

Question 4

What do we vacuum down to?

Answer 4

29.9 mercury

Question 5

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

Answer 5

Open overload

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

Question 6

How do you use an ammeter?

Answer 6

In series

Question 7

What does the Delta T measure for use?

Answer 7

Return air and supply air

Question 8

What is an EMF meter?

Answer 8

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

Question 9

What keeps the compressor running cool?

Answer 9

Cool Suction line vapors

Question 10

What does OL mean?

Answer 10

Openline, Open circuit

Question 11

The winding on the motor are located where?

Answer 11

Stator

Question 12

What component will energize the compressor located in the condenser?

Answer 12

Contactor

Question 13

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

Answer 13

Latent heat

*Latin for hidden. Hidden from the thermometer.

Question 14

42,000 of BTU is how many tons?

Answer 14

3.5 tons

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

Question 15

What is a sensible temperature?

Answer 15

The temperature that we can measure.

Question 16

What is the CFM per ton?

Answer 16

400 CFM per ton

Question 17

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

Answer 17

970 BTU per lbs.

Question 18

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

Answer 18

In series with the start windings.

Question 19

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

Answer 19

Off position

Question 20

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

Answer 20

Electromagnites

Question 21

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

Answer 21

Low voltage, 24V

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

Question 22

How do you condemn a proper grounded compressor?

Answer 22

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

Question 23

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

Answer 23

It reads above atmospheric pressure (14.7psi)

Low side pressure, Atmospheric pressure, vacuum.

Question 24

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

Answer 24

evaporator coil

Question 25

What do we always purge from our manifolds?

Answer 25

No condensable air

Question 26

What is Alternating Current (ac)?

Answer 26

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

Question 27

How do you measure superheat?

Answer 27

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

Question 28

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

Answer 28

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

Question 29

How many windings does a hermetic compressor have?

Answer 29

2

Question 30

How many windings does a 3 phase motor have?

Answer 30

3

Question 31

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

Answer 31

The same. 120 degrees apart.

Question 32

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

Answer 32

Potential Relay also is known as a voltage relay.

Question 33

Two ways a compressor can fail?

Answer 33

Electrical and mechanical.

Question 34

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

Answer 34

Add or remove heat

Question 35

What is thermodynamics rule #1?

Answer 35

Heat is work and work is heat

Question 36

What is thermodynamics rule #2?

Answer 36

Heat travels from hot to cold.

Question 37

What are the terminals of a termostate?

Answer 37

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

Question 38

How do you wire a potential relay?

Answer 38

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.

Question 39

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

Answer 39

Radiation, conduction, or convection.

Question 40

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

Answer 40

Shorted low voltage

Question 41

What has a primary in and secondary out?

Answer 41

transformers

Question 42

How do we measure capacitors?

Answer 42

Using MFD milliFarad

Question 43

What does NC mean?

Answer 43

Normally Closed

Question 44

What does NO mean?

Answer 44

Normally Open

Question 45

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

Answer 45

PSC - Permanent Split Capacitor note: CSCR uses a start capacitor

Question 46

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

Answer 46

Pressure

Question 47

Where are internal overloads located?

Answer 47

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