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THERMOSTATIC EXPANSION VALVES
SYMPTOMS POSSIBLE CAUSE CHECK OR REMEDIES
Superheat is low to normal Unequal evaporator circuit loading Ensure air flow is equally distributed
with low suction pressure through evaporator
Ensure proper piston is inserted into
RCBA or RCHA evaporator coil
distributor
Check for blocked distributor
tubes
Low load or airflow entering Ensure blower is moving proper air
evaporator coil CFM [L/s]
Remove/Correct any air flow
restriction
Superheat and suction Expansion valve is oversized Install correct TEV
pressure fluctuate (valve is hunting)
Sensing bulb is affected by liquid Relocate sensing bulb in another
refrigerant or refrigerant oil flowing position around the circumference of
through suction line the suction line
Unequal refrigerant flow through Ensure proper distributor piston is
evaporator circuits inserted in RCBA or RCHA coil
Ensure sensing bulb is located
properly
Check for blocked distributor
tubes
Improper superheat adjustment Replace TEV or adjust superheat
(only possible with TEV having
superheat adjustment)
Moisture freezing and partially Recover refrigerant, change filter-
blocking TEV drier, evacuate system and
recharge
Valve does not regulate at all External equalizer line not connected Connect equalizer line in proper
or line plugged location, or remove any blockage
Sensing bulb lost its operating charge Replace TEV
Valve body damaged during soldering Replace TEV
or by improper installation
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