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