Metering Devices, Application And Troubleshooting Flashcards
What controls low side float
Liquid level in the low side
What controls high side float
Liquid level in high side
What controls Capillary tube
Pressure difference
What controls automatic expansion valve
Evaporator pressure plus spring
What controls thermostatic expansion valve
Superheat at the outlet of the evaporator
TXV pressure formula
Bulb pressure = spring pressure + evaporator pressure
What does a low side float achieve
Minimum level of liquid in a flooded evaporator. Stops when:
- system equalizes or
- liquid levels raise enough to lift float and shut off inlet
What does a high side float look to achieve
Liquid levels in highside of system. Opens outlet valve to evaporator as liquid levels increase in high side.
What does a capillary tube look to achieve
Pressure difference between high side and low side
What does an automatic expansion valve look to achieve
Maintains constant pressure in evaporator by use of spring pressure + evaporator pressure
What does a Thermostatic Expansion Valve (TXV) look to achieve
Maintains a constant superheat at the evaporator outlet. Bulb pressure = spring pressure + suction pressure (evaporator)
Where are low side floats used
- commercial
- industrial
- low temperature applications
Where are high side floats used
- domestic
- industrial
Where are capillary tube valves used
- domestic self contained units
- package equipment
- LOW TORQUE MOTORS
Where are Automatic Expansion Valves used
- Domestic
- brine systems
Where are TXV’s used
- Commercial air conditioners
- industrial air conditioners
Low side float adaptability to varying loads
Excellent
High side float adaptability to varying loads
Good
Capillary tube adaptability to varying loads
Fair
Automatic expansion valve adaptability to varying loads
Poor
TXV adaptability to varying loads
Excellent
Which two metering controls require a critical charge
High side float and capillary tube
Can a low side float system store refrigerant
Re word question
No
What device must a capillary tube system have
Accumulator
What device muse a capillary tube system NOT have
Reciever
Low side float symptoms of overcharge
Excessive head pressure
Float remains high and allows minimal liquid refrigerant to flow causing high head pressure
Low side float symptom of undercharge
High suction pressure
Low charge causes float to drop allowing high pressure liquid refrigerant to flow freely
High side float symptoms of overcharge
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)
High side float symptoms of undercharge
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)
Capillary tube system symptom of overcharge
Floodback in suction line
Pressure differential is still maintained however high pressure liquid refrigerant is forced through
Capillary tube system symptoms of undercharge
Low head and suction pressures
Tube acts oversized and system equalizes
Automatic expansion valve system symptoms of overcharge
High head pressure
Fully compressed spring will still only allow a certain amount of refrigerant through
Automatic expansion valve system symptom of undercharge
Low head pressure
TXV system symptom of overcharge
High head pressure
Bulb = spring + suction pressure
TXV system symptom of undercharge
Low head pressure and high superheat
Bulb = spring + suction pressure
If suction pressure goes down, valve opens more than usual
Which 3 valves are adjustable in the field
- automatic expansion valve
- TXV
- hand expansion valve
Which two metering devices are used on multiple systems
Low side float and TXV
Do liquid and cross charges have a MOP
No
Do gas and gas cross charges have a MOP
Yes
Where does migration occur
At the coldest spot
What happens to a TXV if the bulb were to rupture
The valve would shut
Bulb pressure = spring pressure + superheat
What is likely cause of cap tube plugging in the first 6”
Desiccant (filter drier break down)
What is likely cause of cap tube plugging in last 6”
Moisture or wax
What does an under capacity valve result in
Starving evaporator
What does over capacity valve result in
Hunting
Where is the valve screen located
Inlet of valve
What is the minimum setting of superheat on an electrical expansion valve
O F degrees and up
What is the proper way to test a TXV seat
Pressurize the outlet and cool the bulb
What type of metering device is used for low torque starting
Cap tube
What device must be used with a cap tube system
Accumulator
What does a TEV maintain
Constant superheat in the evaporator
What is the result of an overcharged AEV system
High head pressure
What happens to sub cooling and average if cap tube is plugged
Subcooling goes up
Amp draw goes down
What is the purpose of a double diaphragm TXV
Limit suction pressure during high load conditions
Rating of TXV
Measured in tons
Function of CPR or CRO and how does it operate
Closes on rise of outlet, maintains max compressor pressure (safety)
Purpose and function of EPR
“Hold back valve” maintains pressure in evaporator. Closes on rise of inlet pressure
Purpose of ORD
Open on rise of differential, maintains 2F degree differential. Used in on condensing unit
Function of ORI
Open on rise of inlet. Like EPR, minimum pressure to receiver
Function of headmaster
(ORI+ORD) maintains head pressure, bypasses condensing unit in cold atmospheric conditions (>70F)
Function of reversing valve
Redirects lines for building heat (evaporator and condensing unit trade places)
Purpose of DPR
Discharge pressure regulator. Max head pressure to Condensing unit. Used with hot gas bypas
3 types of check valves
Ball
Gate
Spring
Sizing of receiver
10% full at any time.
Must carry 125% of system capacity
Another name for EPR
2 temperature valve or “Hold back valve”
3 wire oil control
Line duty
4 wire oil control
Pilot duty
Sizing refrigerant drop in
Pressure at 0F, and at 100F if difference between refrigerants is greater than 50 then you can’t drop in
3 types of filter driers
Loose full
Compressed bead
Solid core
Evaporator CFM/ ton for cooling and heating
400CFM/ton cooling
450CFM/ ton heating
Type of copper used in general
Type K and L
Type of metal for ammonia system
Black iron or stainless steel
No yellow metals
Valve classified type A or D
Bracing temp
840 - 1985F
Purpose of discharge outlet on ammonia TXV
Reduce wire draw
TQ ques
Solenoid valve construction
Soft iron Core and copper
Cap tube length
6-18”
