CLIMATEMASTER TECHNICAL BULLETIN

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
not be adequate flow for the heat pump to
BI-flow TXV to meter refrigerant in both operate.

modes of operation. ClimateMaster Placement of the TXV sensing bulb is also
important. The sensing bulb will attempt to
employs this method on all packaged heat control the temperature of the line to which it
is connected. Therefore the bulb must be
pumps. When diagnosing possible TXV properly located, secured, and insulated.
The sensing bulb must be located on a
problems it may be helpful to reverse the dedicated suction line close to the
compressor. On a heat pump this is the tube
refrigerant flow to assist with the diagnosis. running from the compressor suction inlet to
the reversing valve. On a packaged heat
Geo-thermal and water source heat pumps pump the bulb may be located almost any
are designed to operate through a wide place on this pipe. If the bulb is located on a
range of entering water temperatures that horizontal section the bulb should be placed
will have a direct effect on the unit in the 10:00 or 2:00 position for optimum
refrigerant operating pressures. Therefore performance.
diagnosing TXV problems can be difficult
and uncertain. Through this bulletin The bulb must be secured to the pipe using
ClimateMaster will attempt to offer some a copper strap. Caution must be used when
clarity and certainty when diagnosing tightening the strap. The strap must be tight
possible TXV problems. enough to hold the bulb securely but caution
must be taken not to over-tighten the strap,
FAILURE: The most common failure mode which could dent, bend, collapse or
of a TXV is for the valve to fail closed. otherwise damage the bulb. The use of heat
Typically a TXV will use spring pressure to transfer paste between the bulb and the pipe
close the valve and an opposing pressure, will also help insure optimum performance.
usually from a diaphragm, to open the valve.
The amount of pressure exerted by the
diaphragm will vary depending on the
pressure inside of the sensing bulb. As the
temperature of, and therefore the pressure
within, the bulb decreases the valve will
modulate closed and restrict the refrigerant

1 Rev. 4/05

TB-G004

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
• High refrigerant sub cooling
bulb or capillary. Can be caused by • TXV and/or low pressure tubing

excessive vibration of the capillary frosting.
• Equalizer line condensing and at a
during shipping or unit operation.
lower temperature than the suction line
‰ If the sensing bulb is damaged or if or the equalizer line frosting.
• FP1 faults in the heating mode in
the capillary is cracked or broken the combination with any of the symptoms
listed above
valve will be considered failed and • FP2 faults in the cooling mode in
combination with any of the symptoms
must be replaced. Replacement of listed above

the TXV “power head” or sensing Some symptoms can mimic a failed TXV but
may actually be caused be another
bulb, capillary, diaphragm assembly problem. Before conducting an analysis for a
failed TXV the following must be verified.
is possible on some TXV’s. The
• Proper water flow and water
power head assembly screws on to temperature in the heating mode

most valves but not all are intended • Proper airflow and temperature in the
cooling mode.
to be replaceable. If the assembly is
• Coaxial water coil is clean on the inside.
not intended to be replaceable May require scale check. Applies to
heating mode.
ClimateMaster recommends
• Under charge of refrigerant. Perform
replacement of the entire valve. sub-cooling and superheat calculations.

• Particulate debris within the system. DIAGNOSTICS: When attempting to
There are several possible sources determine if a TXV is failed several tests or
including contaminated components, checks may be required. To properly
tubing, and service tools, or improper conduct these tests the following tools may
techniques such as during brazing be required.
operations and component replacement.
• Refrigerant gauge manifold compatible
‰ Problems associated with particulate with the refrigerant in the system
debris can be compounded by
refrigerant systems that use POE • Digital thermometer, preferably with wire
refrigerant oil. POE oil has solvent leads that can be connected directly to
like properties that will clean the the tubing and insulated
interior surfaces of tubing and
components. Particulates can be • Refrigerant pressure-temperature chart
released from interior surfaces and for the refrigerant used
may migrate to the TXV strainer,
which can lead to plugging of the Rev. 4/05
strainer.

• Corrosive debris within the system. May
happen after a failure such as a
compressor burn out if system was not
properly cleaned.

• Non-Condensables in the system.
Non-Condensables includes any
substance other than the refrigerant or

2

• ClimateMaster IOM for the model of unit TB-G004
being repaired
‰ IMPORTANT: Always know what type
• ClimateMaster AOM for the CXM/DXM of refrigerant is in the system.
electronic heat pump control Alternate refrigerants such as the
EarthPure R410A refrigerant require
To condemn a TXV as failed verify the approved tools that are dedicated to
following: these refrigerants. Many alternative
refrigerants require the use of
• The suction pressure is low and the synthetic lubricants such as POE oil.
valve is non-responsive. The TXV Contamination from mineral oil can
sensing bulb can be removed from the occur if tools used with refrigerants
suction line and warmed by holding in such as R22 are used.
your hand which should result in an
increase in the suction pressure while ‰ WARNING: Alternative refrigerants
the compressor is operating. The may operate at higher pressures than
sensing bulb can also be chilled by refrigerants such as R22. Tools such
immersion in ice water, which should as manifold gauges must be rated to
result in a decrease in the suction withstand the higher pressures.
pressure while the compressor is FAILURE TO USE APPROVED TOOLS
operating. No change in the suction MAY RESULT IN A VIOLENT
pressure would indicate a non- FAILURE OF THE TOOL(S), WHICH
responsive valve. CAN LEAD, TO SEVERE DAMAGE,
INJURY, OR DEATH.
• The suction pressure is LOW AND the
refrigerant sub-cooling is HIGH AND the ‰ IMPORTANT: Due to the hygroscopic
superheat is high. LOW suction nature of the POE oil in EarthPure
pressure, LOW sub-cooling and HIGH and other environmentally friendly
superheat May indicate an under charge refrigerant systems any component
of refrigerant. HIGH sub-cooling and replacement must be conducted in a
LOW superheat may indicate an over very timely manner using caution and
charge of refrigerant. The suction proper service procedure for these
pressure will usually be normal or high if types of refrigerants. A complete
there is an over charge of refrigerant. installation instruction will be
included with each replacement
• The suction pressure is LOW and TXV/filter-drier assembly. It is of
frosting of the valve and/or equalizer line critical importance these instructions
may indicate a failed valve but may also are carefully understood and
be an indicator of an under charge of followed. Failure to follow these
refrigerant. Calculate the sub-cooling instructions can result in a system
and superheat to verify a failed valve or that is contaminated with moisture to
refrigerant charge issue. the extent several filter-drier
replacements may be required to
REPAIR: properly dry the system.

‰ IMPORTANT: Repair to any sealed ‰ CAUTION: Always recover the
refrigerant system requires training refrigerant from the system with
in the use of refrigeration tools and suitable approved tools, recovery
procedures. Repair should only be equipment, and practices prior to
attempted by a qualified service attempting to remove or repair any
technician. A universal refrigerant- TXV.
handling certificate will always be
required. Local and/or state license ‰ NOTE: Most ClimateMaster TXV’s are
or certificate may also be required. designed for a fixed superheat
setting and are therefore considered
3 non-adjustable. Removal of the
bottom cap will not provide access
for adjustment and can lead to

Rev. 4/05

TB-G004

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.

4 Rev. 4/05

TB - G004

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
High refrigerant superheat operating temperatures and pressures
High refrigerant sub cooling chart
TXV and/or low pressure tubing
frosting. X Reduced water flow Check pump operation
Equalizer line condensing or frosting.
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

X X Return air temperature below minimum Space temperature to cold

Excessive fresh air
X Supply air bypassing to return air

stream (zone systems)

X X Insufficient refrigerant charge Locate and repair leak

Conduct superheat and subcooling
analysis

X X Failed or restricted metering device Failed TXV power head, capillary, or
sensing bulb

Plugged TXV strainer

X X Insufficient refrigerant charge Locate and repair leak

X X Improperly located TXV sensing bulb Locate bulb on suction line between
reversing valve and compressor

X X Failed or restricted metering device Failed TXV power head, capillary, or
sensing bulb

Plugged TXV strainer

X X Excessive refrigerant charge Remove refrigerant as needed

Failed or restricted metering device Failed TXV power head, capillary, or

sensing bulb

X Normal operation Plugged TXV strainer
May occur when Entering water temp
is close to minimum

X X Insufficient refrigerant charge Locate and repair leak

X X Failed or restricted metering device Failed TXV power head, capillary, or
sensing bulb

Plugged TXV strainer
X X Failed or restricted metering device Failed TXV power head, capillary, or

sensing bulb

Plugged TXV strainer

Rev 4/05