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Fujitsu FO20R Series Installation Instructions Manual page 71

Variable speed r-410a heat pump outdoor units
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9.12 Service Analyzer Charts (cont.)
ELECTRONIC EXPANSION VALVES (cont.)
SYMPTOM
Unequal evaporator circuit loading
Superheat is low
to normal with low
suction pressure
Low load or airflow entering evaporator coil
Expansion valve is oversized.
Section thermister is affected by liquid refrigerant
or refrigerant oil flowing through suction line
Superheat and
suction pressure
Unequal refrigerant flow through evaporator
fluctuate (valve
circuit
is hunting)
Moisture freezing and partially blocking EXV
Pressure transducer not connected or plugged
Suction line thermistor not connected, or
Valve does not
installed on heat effected zone.
regulate at all
Suction line thermistor failed (continuity to
control, wire damaged, resistance values
incorrect)
9.0 DIAGNOSTICS & TROUBLESHOOTING
POSSIBLE CAUSE
REMEDY
Ensure airflow is equally distributed through
evaporator.
Check for blocked distributor tubes.
Ensure blower is moving proper air CFM.
Remove/Correct any airflow restriction.
Install correct EXV
Relocate sensing bulb in another position around the
circumference of the suction line.
Ensure sensing bulb is located properly.
Check for blocked distributor tubes.
Recover refrigerant, change filter-drier, evacuate
system, and recharge.
Connect pressure transducer in proper location, or
remove any blockage.
Install suction line thermistor in correct horizontal
clean section of copper pipe.
Replace suction line thermistor.
71

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