4 Basic Components Of A Refrigeration System

Front 1

What does the term reciprocating refer to?

Back 1

Transfer of direction of force (from circular motion of crankshaft to the up and down motion of the pistons

Front 2

In a reciprocating compressor what happens when the piston is drawn downward?

Back 2

- Pressure drops

- suction valve opens

- vapour enters cylinder

Front 3

What happens as a piston rises in a reciprocating compressor? What is another term for this motion?

Back 3

- pressure increases

- discharge valve opens

Known as the “compression stroke”

Front 4

Which compressor has a notable design inefficiency?

Back 4

The reciprocating style compressor always leaves a small amount of compressed vapour (known as “clearance volume” ) which must re expand after each compression stroke before the suction valve opens

Front 5

The complete compression cycle of a reciprocating compressor consists of these stages:

Back 5

- suction

- compression

- discharge

Front 6

What style compressor contains:

- internal springs

- suction cooled motor

Back 6

Hermetic

Front 7

What are some of the typical maintenance items on a semi hermetic compressor?

Back 7

- Valve plates

- oil changes

Front 8

What are some unique characteristics of a semi hermetic compressor?

Back 8

- External mounted springs

- bolted shell

- oil pump for lubricatiin

- can be air, suction, or water cooled

Front 9

What is one way to tell if a semi hermetic compressor is suction cooled?

Back 9

Suction intake valve will be located on end of compressor (butt end= opposite end of pistons)… pistons are where the crankshaft is encased. Motor is on other end.

Front 10

Where are the valve plates located on a semi hermetic compressor?

Back 10

With the pistons!

Front 11

Every _________________________ surface within a compressor must be lubricated.

Back 11

load bearing surface

Front 12

How is a crankshaft lubricated within a semi hermetic compressor?

Back 12

Crankshaft is hollow with holes for bearing lubrication

Front 13

Connecting rods in a semi hermetic compressor connect the _______________ to the _____________.

Back 13

Crankshaft > piston

Front 14

Where would you find the service valves on an air cooled compressor?

Back 14

Next to the cylinders

Front 15

Copeland’s _________________ compressor is a redesign of the _________________ style compressor and has improved _____________ valve design as a result of reduced _______________which reduces ________________ of vapour and is more ____________

Back 15

Discus compressor

Reciprocating

Discharge valve

Reduced clearance volume

Reduces reexpansion

More efficient

Front 16

How would you test compressor inefficiency?

Back 16

Front seat the suction service valve. This will isolate the compressor from the suction side of the system but will show on your gauges whether the valves are leaking

Front 17

What is a technical definition of the mid seated position? How would you midseat a valve?

Back 17

Technically 1 full turn clockwise is mid seat.

I would close all the way and count the turns then back off halfway

Front 18

What is compression ratio?

Back 18

Head pressure (absolute) divided by suction presssure (absolute)

Front 19

True or false?

A scroll compressor is more efficient than a reciprocating because it has fewer moving parts.

Back 19

True!

But also because it has NO valves and there is NO clearance volume

Front 20

Is the orbiting scroll in a compressor located on the top or bottom?

Back 20

Orbiting scroll is on the bottom. The fixed scroll is on the top

Front 21

What cools the motor on a scroll compressor and where is the motor located?

Back 21

Suction vapour cools the motor which is located below and coupled to the orbiting scroll

Front 22

What cools the motor on a scroll compressor and where is the motor located?

Back 22

Suction vapour cools the motor which is located below and coupled to the orbiting scroll

Front 23

What style of compression is utilized in vacuum pumps?

Back 23

Rotary style

Front 24

What separates the discharge from the suction vapour in a rotary style compressor?

Back 24

The vane/blade

Front 25

What style compressor receives intake refrigerant from a discharge valve?

Back 25

Rotary style

Front 26

True or false?

Rotary compressors are suction cooled.

Back 26

False. compressed vapour is discharged into the motor cavity which can handle hotter temps.

Front 27

What compression ratio is typically considered to be too high for a hermetic compressor? What is a negative result of these ratios?

Back 27

12:1 is the upper threshold. Above this and compression will generate too much heat which will degrade the oil in the system = burn/ acid formation

Front 28

What solution is generally used in systems requiring high compression ratios?

Back 28

Low temp freezing applications typically use two stage compression (each compressor has a lower compression ratio)

Front 29

List the 5 major styles of compressor used in refrigeration and cooling

Back 29

Reciprocating

Screw

Rotary

Scroll

Centrifugal

Front 30

What types of compressor are typically used in residential and light commercial air conditioning ?

Back 30

Rotary

Scroll

Reciprocating

Front 31

What style compressor is extensively used in large building air conditioning?

Back 31

Centrifugal

Front 32

What style compressor is typically only rated to work at low side/suction pressures?

Back 32

Hermetic

Front 33

What style lubrication is used in hermetic compressors?

Back 33

Splash lubrication for smaller hermetic compressors

Pressure lubrication for larger compressors

Front 34

Hermetic compressors usually have a crankshaft in the ______________ position

Back 34

Vertical

Front 35

Open-drive compressors make use of a ___________ that is either ______________ drive or __________ driven and require a ___________ seal.

Back 35

External Shaft

Direct

Belt

Shaft seal

Front 36

Where is the motor located on a screw type compressor?

Back 36

Exterior/open motor. It makes use of a shaft similar to open drive semi hermetic (serviceable) compressors

Front 37

Name the crankshaft component typically used in straight shaft applications and is similar to a cam lobe

Back 37

An Eccentric

Front 38

In what two styles are connecting rods made for crankshafts ?

Back 38

Off Center throws

Eccentric

Front 39

True or false

Pressure lubrication only works inside a compressor once the system is fully running at working speed.

Back 39

True

Front 40

What are two common styles of valve in compressors? What are their typical shapes?

Back 40

Flapper (reed) valves (shape dependent on manufacturer)

Ring valves (circular)

Front 41

Where is the valve plate typically located in a compressor?

Back 41

Between the compressor head and the top of the cylinder wall

Front 42

True or false?

The compressor heads typically contains both the discharge gas chamber and the suction gas chamber

Back 42

True

Front 43

What is a slang term sometimes attributed to hermetic compressor and why?

Back 43

Tin can compressor

They are typically made of stamped steel and only designed to withstand low side working pressures compared to serviceable/semi hermetics which are made of cast iron

Front 44

What are two common types of motor mounting for compressors?

Back 44

Rigid (external springs)

Spring (internal suspension)

Front 45

What are some issues associated with the two different styles of compressor mounting?

Back 45

Internal springs can come loose (ie during shipping) which can cause noisy startup/shutdown

External springs run the risk of rusting OR are commonly installed incorrectly in field (need to be loosened before installation)

Front 46

What are two typical styles of terminal block on compressors and what are the advantages of each?

Back 46

Fused glass block typical on smaller compressors can withstand more heat but difficult to repair if needed.

Fibre blocks are sealed with an o ring and are easier to replace but have lower heat tolerance

Front 47

List two different styles of motor protection devices on compressors and disadvantages of each

Back 47

Internal overload protectors trip if the unit begins to surge on hermetics and are impossible to access in case of malfunction (stuck open).

Thermistors are used to disrupt the 24 v signal if an overheat situation occurs. No Disadvantages?

Front 48

What would be considered a higher than normal temperature for a discharge gas line on a reciprocating compressor?

Back 48

250 deg f ???

Front 49

Which compressor type uses tapered, machined, gear components to trap the gas for compression?

Back 49

Screw???

Front 50

What would be done to increase the compressor speed on a belt-driven compressor?

Back 50

Decrease drive pulley size???

Front 51

Positive displacement device is another name for which type of compressor?

Back 51

Piston type/reciprocating

It needs to displace the contents of the chamber OR it will stall

Front 52

What is the result of a slight amount of liquid on a compressor?

Back 52

Small amounts of liquid will displace oil / dilute oil which will reduce lubrication and lead to wear and damage (I.e. throw a rod = mechanical failure which will cause burnout)

Front 53

What are some causes of liquid slugging?

Back 53

- metering device over feeding

- insufficient air over evap coil

- low heat load

Front 54

True or false?

Liquid slugging usually causes immediate damage

Back 54

True

Pistons will stall or break if too much liquid is present (liquid is non condensable!)

Front 55

What are ways to keep a refrigeration system operating at peak efficiency?

Back 55

> keep the evaporator clean!

> keep the condenser coil clean

> do not operate the systems at lower ambient temperatures than they are designed for

The main goal with all 3 of these items is to maintain as low a compression ratio as possible. That is why evap coil airflow is more important than condenser coil airflow for maintenance. Poor evaporator parameters has a bigger impact on the ratios

Front 56

Describe how a compressor can be oil free

Back 56

A Centrifugal compressors has magnetically levitated bearings in its rotor which are frictionless.

Front 57

What two components of a reciprocating compressor control/reduce it’s efficiency ?

Back 57

- valve design (too much clearance volume)

- down time between strokes as the chamber refills

Front 58

What are some advantages to modulating capacity?

Back 58

- target temperatures can be better maintained so ambient temps are tighter = lower head temp and lower suction pressure

- lower cycling rate

- flexible demand parameters (I.e. ramp up for high demand situations, ramp down for low demand usage)

Front 59

What makes discus compressors more efficient?

Back 59

- valve design (less clearance vol.)

- larger valve bore = more gas per stroke

- some are modulating

Front 60

List some advantages of scroll type compressors

Back 60

- efficiency (no re-expansion)

- quiet operation

- fewer moving parts

Front 61

List some advantages of scroll type compressors

Back 61

- efficiency (no re-expansion)

- quiet operation, low vibration (no reed valves)

- fewer moving parts

- less transfer of heat between suction and discharge which leads to higher density of vapour leading to increase mass flow rate

- radial movement between the scrolls allows small particles and amounts of liquid (non condensables) to pass between the scrolls without causing damage as the scrolls can move side to side slightly

Centrifugal force allows for leak free contact as long as there is oil

Front 62

What does the term variable compression ratio refer to?

Back 62

Piston type compressors (compression is more of a pulsation unlike scrolls)

Front 63

What does flank sealing refer to?

Back 63

This is the seal that is formed by centrifugal force and lubricating oil between the mating scrolls which prevents gas-pocket leakage. (Also known as axial sealing OR up and down sealing)

Front 64

True or false

There is no need for valves in a scroll compressor

Back 64

False

Scrolls utilize a check valve in the discharge chamber to stop high side gas flowing into the low side on down cycle

Front 65

How is digital capacity control achieved with scroll compressors?

Back 65

Axial separation of the scrolls controlled via a solenoid valve which varies the amount of discharge gas sent back into the suction bypass ports. So on energization the solenoid sends more bypass which unloads the scroll

Front 66

What are some advantages to modulating capacity on a scroll compressor?

Back 66

- improved dehumidification

- reduced cycling (more reliability and reduced power consumption)

- flexible demand parameters

Front 67

List some scroll compressor protection devices

Back 67

- internal fault protector (overload)

- internal pressure relief (opens at 5-625 psi differential for 410)

- floating seal (protects against internal vacuum state which could damage fusite terminal)

- temperature operated disc (TOD) opens at 270 deg f discharge temp

Front 68

How would you increase the compressor speed on a belt driven compressor?

Back 68

- decrease driven pulley size

- increase drive pulley size

Front 69

What is difference between driven and drive pulleys on belt driven compressors?

Back 69

Driven is the pulley on the compressor

Drive is the pulley on the motor

Front 70

What is difference between driven and drive pulleys on belt driven compressors?

Back 70

Driven is the pulley on the compressor

Drive is the pulley on the motor

Front 71

List two fixed motor speeds on a typical belt drive compressor

Back 71

1725 rpm

3450 rpm

Front 72

What is a typical mini split set to fit max temperature limit (to protect compressor oil?)

Back 72

275 deg f

Front 73

At what temp does pump oil begin to cook?

Back 73

320 deg f