The term SUPERHEAT when used in TEV's refers to the difference in what?
Temperature between the Evap Inlet and the Sensing Bulb pg375
A TXV does not regulate the low side pressure, it controls ____________?
The filling of the Evap with refrigerant pg 375
Increasing Superheat too much will ________?
Starve the Evap
Too low a superheat can flood the evap. Too much refrigerant in the evap can result in liquid refrigerant being drawn into the comp. this is known as _________.
Liquid slugging
Pg375. 19th
what is MMS? and what does it mean
Minimal Stable Signal. The best superheat for an Evap that causes the least sensing bulb temp change while the system is running.
The term "Hunting" can also be known as ___________.
Surging
USe an ________ to check motor windings for continuity, shorts and grounds.
Ohmmeter
If a compressor cannot hold a vacuum, this indicates what?
The exhaust valves on the compressor are leaking
When servicing frozen food equipment, use only the best ______ oil.
Low-wax
If a heat pump uses TXV's, what must be in parallel with the TXV's?
Check valves
How do you avoid having check valves running parallel to your TXV valves in a heat pump?
Use a bi-flow TXV
How does a flow check piston work?
It meters refrigerant passing through it in one direction, and moves its piston to allow refrigerant to pass freely in the other direction
The ________ will be flooded during off cycle if the TXV cannot fully close, which could result in ______ _______ the system.
Evaporator, short cycling
Restrictions from ice formations in valves may occur when a _________ is saturated with moisture and releases some back into the refrigerant.
Filter dryer
Two methods to safely and gently melt frozen moisture in a TXV?
Warm rag or heat gun
A problem with a TXV will manifest changes in the __________.
Evaporator
A leaking _______ or ________ in a TXV cannot be repaired.
needle or valve
Servicing EEV's requires knowledge of its _________.
controller
Indications of a clogged screen in an expansion valves inlet are...? 3 things
poor refrigeration, sweating or frosting only near TXV, and the absence of the sound of refrigerant circulating.
The motor section of an EEV is ________ _________.
Hermetically sealed
__________ of a EEV valve is required following service to the valve
Calibration
What is starving the evaporator?
Liquid refrigerant is only present in part of the evaporator.
Pg375. 19th
What are typical internal system components that typically cause problems?
Compressors, filter-driers, metering devices, hot-gas defrost bypass valves and electric defrost resistance heaters.
Never use liquid drying agents in a system equipped with a _____________.
Solid desiccant
Pg488. 19th
Driers absorb water faster at _______ temperatures.
Lower.
pg488. 19th
Undercharged cap-tube system will have what system characteristics.
Low subcooling, condenser temp, head pressure, evaporator temperature and suction pressure
But high superheat and conditioned space temperature
Undercharged TXV system will have what system characteristics?
Lower then normal head pressure, condenser temperature, subcooling, evaporator temp, and suction pressure
But higher then normal conditioned space temperature, superheat and also bubbles in the sight glass
Pg1260. 19th
System with a restricted cap-tube will show what system characteristics?
�Low to normal head pressure
�High subcooling
�Higher then normal conditioned space
�Lower then normal evaporator temperature
�High superheat
�Lower then normal suction pressure
Pg1261. 19th
As a cap tubes restriction increases, an evaporators cooling ability ________.
Decreases
Pg1261. 19th
What are three common restriction problems in a TXV?
Ice formation
Clogged valve
Restricted inlet screen
Pg1262. 19th
What can cause an evap to be flooded during off cycle and possibly short cycle the system?
TXV not fully closing. This can be visibly evident in frosting and sweating of the suction line
Pg1262. 19th
An ice restriction in a TXV often causes low-side pressure to _________.
Fluctuate
Pg1263. 19tg
Will an inefficient compressor exhibit the same characteristics with a TXV and a cap-tube?
Yes
Pg1265. 19th
What are system characteristics for a system with an inefficient compressor?
�lower then normal head pressure and condenser temperature
�Normal sub-cooling
�High superheat
�Higher than normal condition space temp, evap temp and suction temp
Pg1265. 19th
An overcharged cap-tube system with show what characteristics?
�Higher than normal head pressure and condenser temp
�High subcooling
�higher than normal conditioned space temp and evap temp
�Low superheat
�Higher than normal suction pressure
Pg1266. 19th
What characteristics will an overcharged TXV system have?
�Higher than normal head pressure,and condenser temperature.
�High subcooling
�No bubbles
�Higher than normal conditioned space and evap temperature
�Normal superheat
�Higher than normal suction pressure
Pg1267. 19th
TXV system with a restriction in the liquid line will show these characteristics:
Lower than normal head pressure and condenser temp
�Normal subcooling
�Measurable temp drop along liquid line
�Bubbles in sight glass
�Higher then normal conditioned space temp
�Lower than normal evap temp and suction pressure
�High superheat
A system using a TXV having a restriction in the suction line will exhibit what characteristics?
�Lower then normal head pressure and condenser temp
�Low subcooling
Higher than normal conditioned space temp and evap temp �Higher than normal evap pressure
�Low superheat
�High vacuum past the suction line clog.
(Generally a clogged filter-drier)
A likely cause of systems taking longer then normal time to cool products can be ____________.
Non condensables trapped in the condenser
Pg1268. 19th
A cap-tube system with non condensables trapped in its condenser will show these characteristics:
�Higher than normal head pressure and condenser temp
�High subcooling
�Higher than normal conditioned space and evap temp
�Low or no superheat
�Higher than normal suction pressure pg1270. 19th
A TXV system with non-condensables trapped in its condenser with show these characteristics:
�Higher than normal head pressure and condenser temp
�High subcooling
�no bubbles in sight glass
�Higher than normal condition space temp
�normal to high evap temp
�Normal superheat
�higher than normal suction pressure
Pg1271. 19th
What's the quickest way to determine whether a systems condenser has noncondensables ?
Measure and monitor head pressure after shutting off the system. If head pressure does not does not drop immediately, noncondensables are present
Pg1270. 19th
A TXV system with a reduced condenser efficiency will exhibit what characteristics?
�higher than Norman head pressure and Condenser temperature
�Normal subcooling
�no bubbles
�Normalnto high conditioned space temp and evap temp
�normal or low superheat �higher than normal suction pressure
Cap tube system with reduced evap efficiency will show hear characteristics:
�Lower than normal head pressure and condenser temp
�Normal subcooling
�Higher than normal conditioned space temp
�Lower then normal evap temp
�Low or No superheat
�lower than normal suction pressure
Pg1275. 19th
TXV system with reduced evap efficiency will have these characteristics:
Lower than normal head pressure and condenser temp
�Normal subcooling
�No bubbles
�Higher Than normal conditioned space temp
�Lower than normal evap temp
�Normal superheat
�Lower than normal suction pressure
Can a leaking needle or valve in a TXV be repaired?
No, you must replace the entire TXV
Pg1307. 19th
A starved evaporator frosts unevenly and sweats in properly. This problem may be due to:
�Clogged inlet screen in the TXV,
�loss of refrigerant from a TXV's sensing bulb,
�frozen moisture in the TXV,
�wax from the oil accumulating in the TXV,
�needle stuck shut, �under-capacity valve orifice.
Pg1307. 19th
The formation of frost on the evaporator and sometimes on the suction line maybe do too:
The TX V needle maybe leaking, the TXV's sensing bulb maybe attach loosely to the suction line or in-properly located or not properly insulated, dirt or debris maybe stuck in the valve and holding it open, the TXV's inlet screen may be clogged, The TXV ma
Swelling or frosting on the suction line behind the sensing bulb indicates too much refrigerant flow this condition may be caused by
A loose connection between the sensing bulb and suction line, warm air flow over a sensing bulb that is not insulated, pressure drop in the evaporator is too great, TXV needle stuck open or unable to close fully, undersized evaporator, thermal Bulb has wr
An EEV operates similar to a TXV however the plunger pin, which controls refrigerant flow through the valve, is usually operated by a _________.
Small electric motor
Pg1308. 19th
What are the main components for an EEV's operation?
�A stepper motor that moves the plunger
�An Electric temp sensor
�a pressure transducer that provides the controller with pressure levels for so trolling superheat(not all EEV's have this)
�a controller hat processes the sensor data and controls the stepp
Servicing EEV's requires knowledge of its ________.
Controller
Pg1308. 19th
Most EEVs are highly durable and some faults may be a result of ________ failures
Electronic
Pg1308. 19th
A lack of liquid refrigerant is indicated by a ______ evaporator.
Warm
Pg1335. 19th
The motor section of a EEV is ___________ sealed and __________ be serviced.
Hermetically
May not
Pg1336. 19th
The ______ and ______ of an EEV may be serviced, similar to a mechanical valve
Valve body
Pin
Pg1336. 19th