Metering Devices, Application And Troubleshooting

Question 1

What controls low side float

Answer 1

Liquid level in the low side

Question 2

What controls high side float

Answer 2

Liquid level in high side

Question 3

What controls Capillary tube

Answer 3

Pressure difference

Question 4

What controls automatic expansion valve

Answer 4

Evaporator pressure plus spring

Question 5

What controls thermostatic expansion valve

Answer 5

Superheat at the outlet of the evaporator

Question 6

TXV pressure formula

Answer 6

Bulb pressure = spring pressure + evaporator pressure

Question 7

What does a low side float achieve

Answer 7

Minimum level of liquid in a flooded evaporator. Stops when:

• system equalizes or
• liquid levels raise enough to lift float and shut off inlet

Question 8

What does a high side float look to achieve

Answer 8

Liquid levels in highside of system. Opens outlet valve to evaporator as liquid levels increase in high side.

Question 9

What does a capillary tube look to achieve

Answer 9

Pressure difference between high side and low side

Question 10

What does an automatic expansion valve look to achieve

Answer 10

Maintains constant pressure in evaporator by use of spring pressure + evaporator pressure

Question 11

What does a Thermostatic Expansion Valve (TXV) look to achieve

Answer 11

Maintains a constant superheat at the evaporator outlet. Bulb pressure = spring pressure + suction pressure (evaporator)

Question 12

Where are low side floats used

Answer 12

• commercial
• industrial
• low temperature applications

Question 13

Where are high side floats used

Answer 13

• domestic

- industrial

Question 14

Where are capillary tube valves used

Answer 14

• domestic self contained units
• package equipment
• LOW TORQUE MOTORS

Question 15

Where are Automatic Expansion Valves used

Answer 15

• Domestic

- brine systems

Question 16

Where are TXV’s used

Answer 16

• Commercial air conditioners

- industrial air conditioners

Question 17

Low side float adaptability to varying loads

Answer 17

Excellent

Question 18

High side float adaptability to varying loads

Answer 18

Good

Question 19

Capillary tube adaptability to varying loads

Answer 19

Fair

Question 20

Automatic expansion valve adaptability to varying loads

Answer 20

Poor

Question 21

TXV adaptability to varying loads

Answer 21

Excellent

Question 22

Which two metering controls require a critical charge

Answer 22

High side float and capillary tube

Question 23

Can a low side float system store refrigerant

Re word question

Answer 23

No

Question 24

What device must a capillary tube system have

Answer 24

Accumulator

Question 25

What device muse a capillary tube system NOT have

Answer 25

Reciever

Question 26

Low side float symptoms of overcharge

Answer 26

Excessive head pressure | Float remains high and allows minimal liquid refrigerant to flow causing high head pressure

Question 27

Low side float symptom of undercharge

Answer 27

High suction pressure | Low charge causes float to drop allowing high pressure liquid refrigerant to flow freely

Question 28

High side float symptoms of overcharge

Answer 28

Flood back in suction line (Excess liquid refrigerant flows into float tank causing outlet to fully open allowing uncontrolled amounts of liquid refrigerant to flow to suction side)

Question 29

High side float symptoms of undercharge

Answer 29

Low back pressure (Low levels of liquid refrigerant cause the float to drop forcing the outlet to choke the amount of liquid refrigerant flowing to suction side)

Question 30

Capillary tube system symptom of overcharge

Answer 30

Floodback in suction line | Pressure differential is still maintained however high pressure liquid refrigerant is forced through

Question 31

Capillary tube system symptoms of undercharge

Answer 31

Low head and suction pressures | Tube acts oversized and system equalizes

Question 32

Automatic expansion valve system symptoms of overcharge

Answer 32

High head pressure | Fully compressed spring will still only allow a certain amount of refrigerant through

Question 33

Automatic expansion valve system symptom of undercharge

Answer 33

Low head pressure

Question 34

TXV system symptom of overcharge

Answer 34

High head pressure | Bulb = spring + suction pressure

Question 35

TXV system symptom of undercharge

Answer 35

Low head pressure and high superheat | Bulb = spring + suction pressure If suction pressure goes down, valve opens more than usual

Question 36

Which 3 valves are adjustable in the field

Answer 36

- automatic expansion valve - TXV - hand expansion valve

Question 37

Which two metering devices are used on multiple systems

Answer 37

Low side float and TXV

Question 38

Do liquid and cross charges have a MOP

Answer 38

No

Question 39

Do gas and gas cross charges have a MOP

Answer 39

Yes

Question 40

Where does migration occur

Answer 40

At the coldest spot

Question 41

What happens to a TXV if the bulb were to rupture

Answer 41

The valve would shut | Bulb pressure = spring pressure + superheat

Question 42

What is likely cause of cap tube plugging in the first 6”

Answer 42

Desiccant (filter drier break down)

Question 43

What is likely cause of cap tube plugging in last 6”

Answer 43

Moisture or wax

Question 44

What does an under capacity valve result in

Answer 44

Starving evaporator

Question 45

What does over capacity valve result in

Answer 45

Hunting

Question 46

Where is the valve screen located

Answer 46

Inlet of valve

Question 47

What is the minimum setting of superheat on an electrical expansion valve

Answer 47

O F degrees and up

Question 48

What is the proper way to test a TXV seat

Answer 48

Pressurize the outlet and cool the bulb

Question 49

What type of metering device is used for low torque starting

Answer 49

Cap tube

Question 50

What device must be used with a cap tube system

Answer 50

Accumulator

Question 51

What does a TEV maintain

Answer 51

Constant superheat in the evaporator

Question 52

What is the result of an overcharged AEV system

Answer 52

High head pressure

Question 53

What happens to sub cooling and average if cap tube is plugged

Answer 53

Subcooling goes up | Amp draw goes down

Question 54

What is the purpose of a double diaphragm TXV

Answer 54

Limit suction pressure during high load conditions

Question 55

Rating of TXV

Answer 55

Measured in tons

Question 56

Function of CPR or CRO and how does it operate

Answer 56

Closes on rise of outlet, maintains max compressor pressure (safety)

Question 57

Purpose and function of EPR

Answer 57

“Hold back valve” maintains pressure in evaporator. Closes on rise of inlet pressure

Question 58

Purpose of ORD

Answer 58

Open on rise of differential, maintains 2F degree differential. Used in on condensing unit

Question 59

Function of ORI

Answer 59

Open on rise of inlet. Like EPR, minimum pressure to receiver

Question 60

Function of headmaster

Answer 60

(ORI+ORD) maintains head pressure, bypasses condensing unit in cold atmospheric conditions (>70F)

Question 61

Function of reversing valve

Answer 61

Redirects lines for building heat (evaporator and condensing unit trade places)

Question 62

Purpose of DPR

Answer 62

Discharge pressure regulator. Max head pressure to Condensing unit. Used with hot gas bypas

Question 63

3 types of check valves

Answer 63

Ball Gate Spring

Question 64

Sizing of receiver

Answer 64

10% full at any time. | Must carry 125% of system capacity

Question 65

Another name for EPR

Answer 65

2 temperature valve or “Hold back valve”

Question 66

3 wire oil control

Answer 66

Line duty

Question 67

4 wire oil control

Answer 67

Pilot duty

Question 68

Sizing refrigerant drop in

Answer 68

Pressure at 0F, and at 100F if difference between refrigerants is greater than 50 then you can’t drop in

Question 69

3 types of filter driers

Answer 69

Loose full Compressed bead Solid core

Question 70

Evaporator CFM/ ton for cooling and heating

Answer 70

400CFM/ton cooling | 450CFM/ ton heating

Question 71

Type of copper used in general

Answer 71

Type K and L

Question 72

Type of metal for ammonia system

Answer 72

Black iron or stainless steel No yellow metals Valve classified type A or D

Question 73

Bracing temp

Answer 73

840 - 1985F

Question 74

Purpose of discharge outlet on ammonia TXV

Answer 74

Reduce wire draw

Question 75

TQ ques | Solenoid valve construction

Answer 75

Soft iron Core and copper

Question 76

Cap tube length

Answer 76

6-18”