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AIR CONDITIONING & HEAT PUMP SYSTEMS
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AIR FLOW MEASUREMENT CFM
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
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BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of HEATING & COOLING TERMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
FAN NOISES, HVAC
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
TEV installation, testing, troubleshooting & repair guide: this article describes how to install, test, or diagnose problems with a thermostatic expansion valve used on air conditioners or heat pumps or similar refrigeration equipment. These include improper thermostatic valve installation, wrong sensor bulb location, sticking TEVs, whistling TEVs, hunting TEVs and other problems.
We define and explain other refrigeration equipment metering devices including AEVs (Automatic Expansion Valves), manually adjusted expansion valves, capillary tubes and Low Side or High Side refrigerant float valves. Page top sketch of a thermostatic expansion valve is provided courtesy of Carson Dunlop Associates.
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Thermostatic expansion valves (TEVs) are designed to meter refrigerant into the cooling coil at the proper rate. This design can keep the proper dose of refrigerant entering the cooling coil for maximum air conditioning or heat pump system operating efficiency.
TEVs are similar to automatic expansion valves (AEVs) discussed below, but incorporate the signal from a temperature sensor mounted at the end of the evaporator coil
If you are diagnosing a problem with an air conditioner or heat pump and the TEV appears to be involved, check the TEV installation details against the information we list below.
The valve fittings and exterior parts must be thoroughly cleaned before soldering or brazing in order to prevent debris from entering the refrigerant system or valve body.
Protect the TEV from heat during soldering or brazing by wrapping the valve body and head with a wet cloth to give 1/4" to 1/2" of thermal protection, and keep the soldering or brazing torch aimed away from the valve itself.
[Click to enlarge any image]
As with any soldering or brazing job, don't use excessive solder or flux or the excess may flow into the valve or tubing to prevent proper operation.
The thermostatic expansion valve sensing bulb that controls the thermostatic expansion valve is clamped to the refrigerant suction line where it monitors the system's temperature.
The TEV should be installed as close as possible to the air conditioning or heat pump evaporator coil inlet. Sketch of CAPILLARY TUBE defects courtesy of Carson Dunlop. Other TEV and cap-tube defects listed below were obtained from an installation guide for TEV's provided by Singer Controls Corp.
TEV interference: Most installation guides require that the thermostatic expansion valve has nothing else installed on the refrigerant tubing that extends between the TEV and the evaporator coil, except in commercial installations where a refrigerant distributor may have been installed. In this instance (use of a TEV with a refrigerant distributor), the TEV should be a unit that provides an external equalizer.
TEV location height: Do not install the Thermostatic Expansion Valve higher than the liquid refrigerant receiver. If a TEV is placed too high in a commercial system, refrigerant vapor or flash gas from the receiver may enter the TEV and prevent its proper operation.
WAtch out: a TEV sensor that is too loose or has a poor thermal connection to the suction line can send improper signals to the TEV and can cause liquid refrigerant flood damage to the compressor motor. 
Watch out: the TEV's temperature sensing bulb should never be placed at the bottom or under-side of the suction line. That's becausse there may be refreigerant oil along the bottom of the tubing - a condition that will cause improper reading of the line's temperature, thus causing improper TEV operation.
Watch out: the TEV temperature sensing bulb must not be installed after a heat exchanger - another location giving improper signals to the TEV
Watch out: the TEV temperature sensing bulb must also not be installed close to compoents of large mass (such as a stop valve onthe refrigerant line) because the large mass will influence nearby refrigerant line temperatures, giving the sensor bulb misleading information and causing it to misinform the TEV itself.
Watch out: don't install TEV temperature sensing bulbs on vertical piping and do not install the sensor bulb on a collection tube or riser or even on a horizontal section of tubing that may be located after an oil pocket location such as at a dip or effectively a plumbing trap formed in the refrigerant line.
Watch out: don't install the TEV sensing bulb after a liquid lock. The bulb must be ahead of any liquid lock on the piping system.
On commercial cooling installations it is also important that the TEV be installed in a location leaving enough access to adjust the device. Details about TEV adjustment are below at Adjusting the Thermostatic Expansion Valve
Hunting Thermostatic Expansion Valves can damage the air conditioning or heat pump compressor:
Causes of Refrigerant Floodback in air conditioners, heat pumps, refrigeration equipment
After installing a TEV the system must be tested for leaks using dry nitrogen;
Technical note about TEVs and refrigerant pressure: TEVs do not maintain pressure on the low side of the refrigeration system. The TEV keeps refrigerant flowing into the cooling coil to keep the superheat level as specified across the cooling coil.
On refrigeration systems that include a liquid refrigerant receiver and as long as there is adequate level of refrigerant in the system and the TEV is working, the refrigerant charge amount is not absolutely critical.
Relationship between TEVs and Compressor/Condenser motors
When a TEV is installed on refrigeration equipment we need a heavier (more powerful) compressor motor since the compressor has to start against a head pressure.
TEVs and long evaporator coils
On systems that use a long evaporator coil, and equalizer may be used to offset the large pressure drop that occurs across the long evaporator coil. This added feature assures that pressure in the valve and at the end of the condenser are equal so that just superheat (and not the pressure drop) operates the TEV.
TEV Sensor element leak problems
Perhaps the main problem that occurs with TEVs is that the valve stops working due to loss of refrigerant in its sensing device. the Thermostatic Expansion Valve sensor element along with its small diameter tubing is a closed system that contains a refrigerant too - the same refrigerant as that used in the system for which the TEV is designed.
The TEV and also AEVs depend on a little oil or oil mist flowing along with refrigerant to lubricate the interior of the valve. But we suspect that a more common cause of TEV valve sticking is the freezing of a droplet of water at the needle valve, holding it stuck. The valve stops working properly.
Sticking TEVs are discussed separately at TEV STICKING REPAIR
Capillary Tube problems: see our separate article detailing the inspection, installation, and repair or replacement of CAPILLARY TUBES
Watch out: water or dirt in the refrigerant piping system can cause serious and costly problems in the TEV or cap tube that impact the entire refrigeration system.
Because differences in temperature in and around the cooling equipment can affect the TEV's operation, in commercial cooling installations the Thermostatic Expansion Valve has to be placed where its sensor, usually located in the top or "head" of the TEV, will be warmer than the thermal bulb which controls the device. Otherwise liquid refrigerant may be improperly discharged by the valve.
Thermostatic expansion valves are rated in tons of refrigeration capacity based on the size of the metering orifice in the device. The TEV (or AEV) must be matched to the capacity of the cooling system (actually the coil) and to the specific refrigerant used, since at any given temperature different refrigerants will exert different pressures in the system.
At THERMOSTATIC EXPANSION VALVES we discuss identification, label decoding, and selection of TEVs.
HVACR Thermostatic Expansion Valves - TEVs: this air conditioning repair article series explains the function and installation of all types of refrigerant metering devices, beginning with the most-common thermostatic expansion valve or TEV (or thermal expansion valve) that controls release of refrigerant into the evaporator coil of an air conditioning or heat pump system.
Continue reading at LOST COOLING CAPACITY - the air conditioning system seems to be "running" but not enough cool air, or no cool air at all is being delivered to the occupied space. or select a topic from the More Reading links shown below.
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