Carrier Aquazone 50PTH024 Installation, Start-Up And Service Instructions Manual page 57

Causes of TXV Failure
The most common causes of TXV failure are:
1. A cracked, broken, or damaged sensing bulb or capillary can
be caused by excessive vibration of the capillary during ship-
ping or unit operation.
If the sensing bulb is damaged or if the capillary is cracked or
broken, the valve will be considered failed and must be
replaced. Replacement of the TXV "power head" or sensing
bulb, capillary, diaphragm assembly is possible on some
TXVs. The power head assembly screws onto most valves,
but not all are intended to be replaceable. If the assembly is
not replaceable, replace the entire valve.
2. Particulate debris within the system can be caused by several
sources including contaminated components, tubing, and ser-
vice tools, or improper techniques used during brazing opera-
tions and component replacement.
Problems associated with particulate debris can be com-
pounded by refrigerant systems that use POE (polyol ester
oil). POE oil has solvent-like properties that will clean the
interior surfaces of tubing and components. Particulates can
be released from interior surfaces and may migrate to the
TXV strainer, which can lead to plugging of the strainer.
3. Corrosive debris within the system may happen after a fail-
ure, such as a compressor burn out, if system was not prop-
erly cleaned.
4. Noncondensables may be present in the system. Non-con-
densables includes any substance other than the refrigerant or
oil such as air, nitrogen, or water. Contamination can be the
result of improper service techniques, use of contaminated
components, and/or improper evacuation of the system.
Symptoms
The symptoms of a failed TXV can be varied and will include one
or more of the following:
1. Low refrigerant suction pressure.
2. High refrigerant superheat.
3. High refrigerant subcooling.
4. TXV and/or low pressure tubing frosting.
5. Equalizer line condensing and at a lower temperature than the
suction line or the equalizer line frosting.
6. FP1 faults in the heating mode in combination with any of the
symptoms listed above.
7. FP2 faults in the cooling mode in combination with any of the
symptoms listed above. Some symptoms can mimic a failed
TXV but may actually be caused be another problem.
Before conducting an analysis for a failed TXV the following
must be verified:
1. Confirm that there is proper water flow and water tempera-
ture in the heating mode.
2. Confirm that there is proper airflow and temperature in the
cooling mode.
3. Ensure coaxial water coil is clean on the inside; this applies to
the heating mode and may require a scale check.
4. Refrigerant may be undercharged. To verify, subcooling and
superheat calculations may be required.
Diagnostics
Several tests may be required to determine if a TXV has failed.
The following tools may be required for testing:
1. Refrigerant gauge manifold compatible with the refrigerant in
the system.
2. Digital thermometer, preferably insulated, with wire leads
that can be connected directly to the tubing.
3. Refrigerant pressure-temperature chart for the refrigerant
used.
To determine that a TXV has failed, verify the following:
1. The suction pressure is low and the valve is non-responsive.
2. The TXV sensing bulb can be removed from the suction line
and warmed by holding the bulb in your hand. This action
should result in an increase in the suction pressure while the
compressor is operating. The sensing bulb can also be chilled
by immersion in ice water, which should result in a decrease
in the suction pressure while the compressor is operating. No
change in the suction pressure would indicate a non-respon-
sive valve.
3. Simultaneous LOW suction pressure, HIGH refrigerant sub-
cooling and HIGH superheat.
4. LOW suction pressure, LOW subcooling and HIGH super-
heat may indicate an undercharge of refrigerant. HIGH sub-
cooling and LOW superheat may indicate an overcharge of
refrigerant. The suction pressure will usually be normal or
high if there is an overcharge of refrigerant.
5. LOW suction pressure and frosting of the valve and/or equal-
izer line may indicate a failed valve. However, these symp-
toms may also indicate an undercharge of refrigerant.
Calculate the subcooling and superheat to verify a failed
valve or refrigerant charge issue.
Repair
Puron refrigerant (R-410A) operates at higher pressure than
®
R-22, which is found in other WSHPs. Tools such as manifold
gauges must be rated to withstand the higher pressures. Failure
to use approved tools may result in a failure of tools, which
can lead to severe damage to the unit, injury or death.
Most TXVs are designed for a fixed superheat setting and are
therefore considered non-adjustable. Removal of the bottom
cap will not provide access for adjustment and can lead to
damage to the valve or equipment, unintended venting of re-
frigerant, personal injury, or possibly death.
Always recover the refrigerant from the system with suitable
approved tools, recovery equipment, and practices prior to at-
tempting to remove or repair any TXV.
Use caution when tightening the strap. The strap must be tight
enough to hold the bulb securely but caution must be taken not
to over-tighten the strap, which could dent, bend, collapse or
otherwise damage the bulb.
Puron ® refrigerant (R-410A) requires the use of synthetic lu-
bricant (POE oil). Do not use common tools on systems that
contain R-22 refrigerants or mineral oil. Contamination and
failure of this equipment may result.
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WARNING
WARNING
CAUTION
CAUTION
CAUTION