Carrier Aquazone 50PTH036 Installation, Start-up And Service Instructions Manual

Also see for Aquazone 50PTH024: Installation, Start-Up and Service Instructions

31Causes of TXV Failure — The most common causes of TXVfailure are:1. A cracked, broken, or damaged sensing bulb or capillarycan be caused by excessive vibration of the capillary dur-ing shipping or unit operation.If the sensing bulb is damaged or if the capillary iscracked or broken, the valve will be considered failed andmust be replaced. Replacement of the TXV “power head”or sensing bulb, capillary, diaphragm assembly is possi-ble on some TXVs. The power head assembly screwsonto most valves, but not all are intended to be replace-able. If the assembly is not replaceable, replace the entirevalve.2. Particulate debris within the system can be caused by sev-eral sources including contaminated components, tubing,and service tools, or improper techniques used duringbrazing operations and component replacement.Problems associated with particulate debris can be com-pounded by refrigerant systems that use POE (polyol es-ter oil). POE oil has solvent-like properties that will cleanthe interior surfaces of tubing and components. Particu-lates can be released from interior surfaces and may mi-grate to the TXV strainer, which can lead to plugging ofthe strainer.3. Corrosive debris within the system may happen after afailure, such as a compressor burn out, if system was notproperly cleaned.4. Noncondensables may be present in the system. Non-condensables includes any substance other than therefrigerant or oil such as air, nitrogen, or water. Contami-nation can be the result of improper service techniques,use of contaminated components, and/or improper evacu-ation of the system.Symptoms — The symptoms of a failed TXV can be variedand will include one or more of the following:• Low refrigerant suction pressure• High refrigerant superheat• High refrigerant subcooling• TXV and/or low pressure tubing frosting• Equalizer line condensing and at a lower temperaturethan the suction line or the equalizer line frosting• FP1 faults in the heating mode in combination with anyof the symptoms listed above• FP2 faults in the cooling mode in combination with anyof the symptoms listed above. Some symptoms canmimic a failed TXV but may actually be caused beanother problem.Before conducting an analysis for a failed TXV the follow-ing must be verified:• Confirm that there is proper water flow and water tem-perature in the heating mode.• Confirm that there is proper airflow and temperature inthe cooling mode.• Ensure coaxial water coil is clean on the inside; thisapplies to the heating mode and may require a scalecheck.• Refrigerant may be undercharged. To verify, subcoolingand superheat calculations may be required.Diagnostics — Several tests may be required to determine ifa TXV has failed. The following tools may be required fortesting:1. Refrigerant gage manifold compatible with the refriger-ant in the system.2. Digital thermometer, preferably insulated, with wire leadsthat can be connected directly to the tubing.3. Refrigerant pressure-temperature chart for the refrigerantused.To determine that a TXV has failed, verify the following:• The suction pressure is low and the valve is non-respon-sive. The TXV sensing bulb can be removed from thesuction line and warmed by holding the bulb in yourhand. This action should result in an increase in the suc-tion pressure while the compressor is operating. Thesensing bulb can also be chilled by immersion in icewater, which should result in a decrease in the suctionpressure while the compressor is operating. No change inthe suction pressure would indicate a nonresponsivevalve.• Simultaneous LOW suction pressure, HIGH refrigerantsubcooling and HIGH superheat.• LOW suction pressure, LOW subcooling and HIGHsuperheat may indicate an undercharge of refrigerant.HIGH subcooling and LOW superheat may indicate anovercharge of refrigerant. The suction pressure will usu-ally be normal or high if there is an overcharge of refrig-erant.SUCTIONCOMPRESSORDISCHARGECOAXEXPANSIONVALVEFP2 FP1LIQUIDLINE WATER IN WATER OUTCONDENSATEOVERFLOW(CO)AIR COILFREEZEPROTECTIONWATERCOILPROTECTIONTHERMISTOR(°F) (°F)AIRCOILAIRFLOW AIRFLOWLEGENDFig. 25 — FP1 and FP2 Thermistor LocationCOAX — Coaxial Heat ExchangerAirflowRefrigerant Liquid Line Flow