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Controls Midterm > 104C > Flashcards

104C Flashcards

1
Q

Refrigeration control components include

A

Relays
Thermostats
Pressure controls
Contactors
Heaters
Solenoid valves

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2
Q

What is a constant cut in thermostat

A

Are electromechanical two position thermostats with a factory cut in temperature and an adjustable difference

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3
Q

Thermo dial thermostats are for

A

Medium and low temperature refrigeration they have a set cut in and out

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4
Q

What is a two position thermostat used to do

A

Help maintain stable temperature conditions within a space

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5
Q

What’s the difference between a constant cut in and out

A

Controller differential/ controller range

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6
Q

Above and below the controller differential is what space

A

over shoot
Under short

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7
Q

A controlled temperature is always

A

Rising or falling never the same

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8
Q

Electronic two position on/off thermostats operate the

A

Refrigeration cycle to maintain an acceptable space temperature

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9
Q

What is deviation

A

The length of time it takes for the control point and the set point to equalize

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10
Q

What is offset

A

A sustained difference between the control point and the set point

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11
Q

What is differential

A

The actual separation between the cut in and cut out temperature or pressures in a two position control

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12
Q

Three basic pressure control actions

A

-Open a circuit on a rise in pressure and close on a fall in pressure
-open or close a circuit based on a predetermined pressure difference

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13
Q

4 types of pressure controllers

A

Low pressure controller
High pressure controller
Dual pressure controller
Oil pressure controller

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14
Q

Low pressure controllers have two main functions

A

1.)operate the condensing unit as part of the pump our or pump down cycle
2.) shuts off the condensing unit if the system is short of refrigerant

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15
Q

Difference between a high pressure and low pressure controller

A

High pressure has higher numbers
a reset button
Acts as saftey

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16
Q

High pressure controllers have an

A

Open On rise of inlet

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17
Q

Cheapest controller is a

A

Fan speed controller

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18
Q

An excapsulated pressure controller comes with a

A

Fixed set point and a fixed differential

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19
Q

Oil failure controls help protect refrigeration compressors with built in oil pumps from damage that insufficient lubricant causes
(True or false)

A

True

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20
Q

How does An oil failure control (OFC) help a compressor with positive oil lubrication

A

It stops the compressor if the oil pump fails

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21
Q

Do you add oil if it’s not found in the crank case and there is no leak in the system

A

No it will damage the compressor

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22
Q

Relays and contractor are both

A

Electromagnetic switches in medium and low temp refrigeration circuits

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23
Q

Contactors are usually.

A

Normally open(NO)
Normally closed (NC)

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24
Q

Common coil voltage is available at

A

24V
120V
240V

25
Q

Two time delay actions found in electronic and electromagnetic timers

A

Delay on make
Delay on break

26
Q

Delay on make timer sequences

A

Two or more compressors making sure they don’t start at the exact same time or the cuircut breaker trips

27
Q

What does a Delay on break timer do

A

Prevents the compressor from starting to soon and lets it cool off

28
Q

Electronic delay on make timer provides

A

A time delay in the starting sequence of a multi stage condensing unit

29
Q

Electronic delay on break timer allows

A

Current to flow to the load immediately upon reemerge the input terminal

30
Q

Solenoid valves are

A

Electromagnetically actuated fluid flow control valves usually low or medium temp

31
Q

Valve stems on solenoid valves use

A

Ferrous metals (magnetic)

32
Q

Do you energize a solonoud valve after disconnecting it

A

Never!!!

33
Q

Electronic control Valves

A

Start, stop and regulate refrigerant flow through the system

34
Q

Electronic control valves are also know as

A

Expansion valves
Evaporator pressure regulator

35
Q

Do evaporator pressure regulators work with solenoid valves?

A

Only sometimes but can be solo

36
Q

Evaporator pressure regulator operate on a

A

Open on rise of inlet

37
Q

5 types of heaters

A

Defrost heater
Condensate pan heater
Drain line heater
Mullion heater
Crankcase heater

38
Q

Crankcase heaters prevent

A

Slugging and recking a compressor

39
Q

Oil return problems are more commonly found in

A

Low temperature refrigeration systems

40
Q

Why do low refrigerant systems have frequently poor oil return

A

Due to the low density refrigerant suction Vapour and physically thicker oil

41
Q

Pump down and pump out control cycles does what

A

Removes liquid refrigerant between the liquid line solenoid and the compressor before the compressor can cycle off

42
Q

Only compressor that use a mechanical oil pump have

A

An oil failure control

43
Q

Why do low temp refrigeration systems usually include a crank case heater

A

Reduce refrigerant migration and oil froth build up

44
Q

When oil gets to cold it

A

Boils the refrigerant out of it

45
Q

EPR stands for

A

Evaporator pressure reducer

46
Q

CPR is

A

Compressor pressure regulator

47
Q

Medium temp refrigeration systems usually have crank case heaters only when

A

The compressor is in a cold equipment room or outdoors

48
Q

Is it considered a good practice to employ a crankcase heater

A

Yes

49
Q

What is harder to start a low temp or medium temp system

A

Low is a lot more difficult because of the massive pressure difference

50
Q

Methods of preventing low temp compressor motors from overloading on start up include

A

-Use a delay on break
-Implementation of a pump out control circuit
-application of compressor capacity control methods instead of on/off
-installation of a close on rise of outlet pressure valve to limit suction pressure

51
Q

EPR is always set to

A

Temperature rise on evaporator

52
Q

CPR is set to

A

Amp draw of compressor

53
Q

CRO stands for

A

Close on rise of inlet

54
Q

ORI stands for

A

Open on rise of inlet

55
Q

A receiver is always stored at

A

90% full at 90°F

56
Q

Are pump down systems used on indoor medium temp refrigeration systems larger then 5 tonnes

A

-Rarly usually not
-The short cycle overheats the compressor
-Delay on break helps this

57
Q

What are the two shorts

A

-Winding to winding
-winding to ground/deadshort

58
Q

What does the high limit do in a defrost

A

Prevents damage to the evaporator

59
Q

Refrigeration control system designers may employ a pump out motor on a larger low temp installations because

A

Big compressor motors are less tolerant of multiple starts within a short period of time

Controls Midterm (5 decks)

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