TXV Diagnostic and Replacement Guidelines
TB-G004
TECHNICAL SERVICE BULLETIN
DATE: 18, April 2005
SCOPE: Informative bulletin relating to Thermostatic Expansion Valve diagnostics
PURPOSE: TXV diagnostic and replacement guidelines.
Thermostatic Expansion Valves are used as flow through the valve. The result is less a means of metering the refrigerant in many refrigerant in the evaporator and an increase different types of refrigeration systems. in the superheat. As the temperature at the ClimateMaster uses TXV’s in most of our bulb increases the diaphragm pressure will heat pump products. The purpose of a TXV increase, opening the valve allowing more is to meter the refrigerant through the refrigerant flow and the superheat will be evaporator to achieve a preset superheat at reduced. the TXV sensing bulb. Correct superheat of the refrigerant is important for the most If the sensing bulb, connecting capillary, or efficient operation of the unit and for the life diaphragm assembly become damaged the of the compressor. Therefore correct pressure will be lost and the spring will force operation of the TXV is equally important. the valve to a closed position. The TXV will typically not close completely so some Packaged heat pumps will typically use one refrigerant flow will be normal although it will BI-flow TXV to meter refrigerant in both not be adequate flow for the heat pump to modes of operation. ClimateMaster operate. employs this method on all packaged heat pumps. When diagnosing possible TXV Placement of the TXV sensing bulb is also problems it may be helpful to reverse the important. The sensing bulb will attempt to refrigerant flow to assist with the diagnosis. control the temperature of the line to which it is connected. Therefore the bulb must be Geo-thermal and water source heat pumps properly located, secured, and insulated. are designed to operate through a wide The sensing bulb must be located on a range of entering water temperatures that dedicated suction line close to the will have a direct effect on the unit compressor. On a heat pump this is the tube refrigerant operating pressures. Therefore running from the compressor suction inlet to diagnosing TXV problems can be difficult the reversing valve. On a packaged heat and uncertain. Through this bulletin pump the bulb may be located almost any ClimateMaster will attempt to offer some place on this pipe. If the bulb is located on a clarity and certainty when diagnosing horizontal section the bulb should be placed possible TXV problems. in the 10:00 or 2:00 position for optimum performance. FAILURE: The most common failure mode of a TXV is for the valve to fail closed. The bulb must be secured to the pipe using Typically a TXV will use spring pressure to a copper strap. Caution must be used when close the valve and an opposing pressure, tightening the strap. The strap must be tight usually from a diaphragm, to open the valve. enough to hold the bulb securely but caution The amount of pressure exerted by the must be taken not to over-tighten the strap, diaphragm will vary depending on the which could dent, bend, collapse or pressure inside of the sensing bulb. As the otherwise damage the bulb. The use of heat temperature of, and therefore the pressure transfer paste between the bulb and the pipe within, the bulb decreases the valve will will also help insure optimum performance. modulate closed and restrict the refrigerant
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The bulb must also be properly insulated to oil and can include air, nitrogen, or water. eliminate any influence on the valve Contamination can be the result of improper operation by the surrounding conditions. service techniques, use of contaminated Cork tape is the recommended insulation as components, and/or improper evacuation of it can be molded tight to the bulb and sealed the system. to prevent air infiltration. SYMPTOMS: The symptoms of a failed CAUSES: There are any numbers of valve can be varied and will include one or reasons why a TXV can fail. The most more of the following; common causes are; • Low refrigerant suction pressure • Cracked, broken, or damaged sensing • High refrigerant superheat bulb or capillary. Can be caused by • High refrigerant sub cooling excessive vibration of the capillary • TXV and/or low pressure tubing during shipping or unit operation. frosting. If the sensing bulb is damaged or if • Equalizer line condensing and at a the capillary is cracked or broken the lower temperature than the suction line valve will be considered failed and or the equalizer line frosting. must be replaced. Replacement of • FP1 faults in the heating mode in the TXV “power head” or sensing combination with any of the symptoms bulb, capillary, diaphragm assembly listed above is possible on some TXV’s. The • FP2 faults in the cooling mode in power head assembly screws on to combination with any of the symptoms most valves but not all are intended listed above to be replaceable. If the assembly is not intended to be replaceable Some symptoms can mimic a failed TXV but ClimateMaster recommends may actually be caused be another replacement of the entire valve. problem. Before conducting an analysis for a failed TXV the following must be verified. • Particulate debris within the system. There are several possible sources • Proper water flow and water including contaminated components, temperature in the heating mode tubing, and service tools, or improper • Proper airflow and temperature in the techniques such as during brazing cooling mode. operations and component replacement. • Coaxial water coil is clean on the inside. Problems associated with particulate May require scale check. Applies to debris can be compounded by heating mode. refrigerant systems that use POE • Under charge of refrigerant. Perform refrigerant oil. POE oil has solvent sub-cooling and superheat calculations. like properties that will clean the interior surfaces of tubing and DIAGNOSTICS: When attempting to components. Particulates can be determine if a TXV is failed several tests or released from interior surfaces and checks may be required. To properly may migrate to the TXV strainer, conduct these tests the following tools may which can lead to plugging of the be required. strainer. • Refrigerant gauge manifold compatible • Corrosive debris within the system. May with the refrigerant in the system happen after a failure such as a compressor burn out if system was not • Digital thermometer, preferably with wire properly cleaned. leads that can be connected directly to the tubing and insulated • Non-Condensables in the system. • Refrigerant pressure-temperature chart Non-Condensables includes any for the refrigerant used substance other than the refrigerant or
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• ClimateMaster IOM for the model of unit IMPORTANT: Always know what type being repaired of refrigerant is in the system. • ClimateMaster AOM for the CXM/DXM Alternate refrigerants such as the electronic heat pump control EarthPure R410A refrigerant require approved tools that are dedicated to To condemn a TXV as failed verify the these refrigerants. Many alternative following: refrigerants require the use of synthetic lubricants such as POE oil. • The suction pressure is low and the Contamination from mineral oil can valve is non-responsive. The TXV occur if tools used with refrigerants sensing bulb can be removed from the such as R22 are used. suction line and warmed by holding in your hand which should result in an WARNING: Alternative refrigerants increase in the suction pressure while may operate at higher pressures than the compressor is operating. The refrigerants such as R22. Tools such sensing bulb can also be chilled by as manifold gauges must be rated to immersion in ice water, which should withstand the higher pressures. result in a decrease in the suction FAILURE TO USE APPROVED TOOLS pressure while the compressor is MAY RESULT IN A VIOLENT operating. No change in the suction FAILURE OF THE TOOL(S), WHICH pressure would indicate a non- CAN LEAD, TO SEVERE DAMAGE, responsive valve. INJURY, OR DEATH.
• The suction pressure is LOW AND the IMPORTANT: Due to the hygroscopic refrigerant sub-cooling is HIGH AND the nature of the POE oil in EarthPure superheat is high. LOW suction and other environmentally friendly pressure, LOW sub-cooling and HIGH refrigerant systems any component superheat May indicate an under charge replacement must be conducted in a of refrigerant. HIGH sub-cooling and very timely manner using caution and LOW superheat may indicate an over proper service procedure for these charge of refrigerant. The suction types of refrigerants. A complete pressure will usually be normal or high if installation instruction will be there is an over charge of refrigerant. included with each replacement TXV/filter-drier assembly. It is of • The suction pressure is LOW and critical importance these instructions frosting of the valve and/or equalizer line are carefully understood and may indicate a failed valve but may also followed. Failure to follow these be an indicator of an under charge of instructions can result in a system refrigerant. Calculate the sub-cooling that is contaminated with moisture to and superheat to verify a failed valve or the extent several filter-drier refrigerant charge issue. replacements may be required to properly dry the system. REPAIR: CAUTION: Always recover the IMPORTANT: Repair to any sealed refrigerant from the system with refrigerant system requires training suitable approved tools, recovery in the use of refrigeration tools and equipment, and practices prior to procedures. Repair should only be attempting to remove or repair any attempted by a qualified service TXV. technician. A universal refrigerant- handling certificate will always be NOTE: Most ClimateMaster TXV’s are required. Local and/or state license designed for a fixed superheat or certificate may also be required. setting and are therefore considered non-adjustable. Removal of the bottom cap will not provide access for adjustment and can lead to
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damage to the valve or equipment, For further information contact the unintended venting of refrigerant, ClimateMaster Technical Service Dept. at personal injury, or possibly death. 800-299-9747.
• Use the table below to determine proper unit operating pressures and temperatures. At some conditions low refrigerant suction pressure may be normal. Chart is for model GS/GR heat pumps. Other models may vary. Refer to unit IOM for different models.
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WATER SOURCE HEAT PUMP TXV TROUBLESHOOTING GUIDE
SYMPTOM HTG CLG CAUSE DIAGNOSIS/REPAIR Low refrigerant suction pressure X Normal Operation Check/compare with unit IOM typical operating temperatures and pressures chart
X Reduced water flow Check pump operation Check strainer or filter Improper flow regulator X Water temperature out of range Bring water temperature within proper range X Scaling in water to refrigerant heat Conduct water quality analysis exchanger X Reduced air flow Check for dirty air filter Check for dirty air coil Check fan motor operation External static pressure exceeds fan operating parameters XXReturn air temperature below minimum Space temperature to cold Excessive fresh air X Supply air bypassing to return air stream (zone systems) XXInsufficient refrigerant charge Locate and repair leak Conduct superheat and subcooling analysis XXFailed or restricted metering device Failed TXV power head, capillary, or sensing bulb Plugged TXV strainer High refrigerant superheat XXInsufficient refrigerant charge Locate and repair leak XXImproperly located TXV sensing bulb Locate bulb on suction line between reversing valve and compressor XXFailed or restricted metering device Failed TXV power head, capillary, or sensing bulb
Plugged TXV strainer High refrigerant sub cooling XXExcessive refrigerant charge Remove refrigerant as needed Failed or restricted metering device Failed TXV power head, capillary, or sensing bulb
Plugged TXV strainer TXV and/or low pressure tubing X Normal operation May occur when Entering water temp frosting. is close to minimum XXInsufficient refrigerant charge Locate and repair leak XXFailed or restricted metering device Failed TXV power head, capillary, or sensing bulb Plugged TXV strainer Equalizer line condensing or frosting. XXFailed or restricted metering device Failed TXV power head, capillary, or sensing bulb Plugged TXV strainer
Rev 4/05